JP2020194625A - Manufacturing method of battery carbon nanotube dispersion composition - Google Patents

Abstract

To provide a method for producing a carbon nanotube dispersion composition having excellent conductivity and high productivity.SOLUTION: A manufacturing device of battery carbon nanotube dispersion composition including a carbon nanotube, a dispersant, and an aqueous liquid media includes a step of dispersion treatment using a bead mill (step A), the carbon nanotubes are continuously or discontinuously added until the carbon nanotube concentration in the carbon nanotube dispersion composition for a battery reaches a target value, and before or at the same time as the addition of the carbon nanotubes, the dispersant is added, and the diameter of the beads of the bead mill is in the range of 0.01 to 1.25 mm.SELECTED DRAWING: None

Description

The present invention relates to a method for producing a carbon nanotube dispersion composition for a battery, which has high conductivity and high productivity by performing a dispersion treatment without crushing or damaging the carbon nanotubes more than necessary.

With the widespread use of electric vehicles, the reduction in size and weight of mobile devices, and the increase in performance, secondary batteries having a high energy density and the capacity of the secondary batteries are required to be increased. Against this background, non-aqueous electrolyte secondary batteries that use non-aqueous electrolytes have come to be used in many devices due to their characteristics of high energy density and high voltage, and lithium-ion secondary batteries are particularly attracting attention. ing.

As the negative electrode material used for the lithium ion secondary battery, a carbon material typified by graphite having a low potential close to that of lithium (Li) and a large charge / discharge capacity per unit mass is used. However, these electrode materials are used to the point where the charge / discharge capacity per mass is close to the theoretical value, and the energy density of the battery is approaching the limit. Therefore, attempts have been made to reduce conductive materials and binders that do not contribute to the discharge capacity inside the battery.

As the conductive material, carbon-based fillers such as carbon black, Ketjen black, fullerene, graphene, and fine carbon materials are used. In particular, carbon nanotubes, which are a type of fine carbon fibers, are often used. For example, by adding carbon nanotubes to graphite or silicon negative electrodes, electrode resistance can be reduced, battery load resistance can be improved, electrode strength can be increased, and electrode expansion / contraction properties can be increased to increase lithium ions. The cycle life of the secondary battery is improved (see, for example, Patent Documents 1, 2 and 3). Further, studies have been conducted to reduce the electrode resistance by adding carbon nanotubes to the positive electrode (see, for example, Patent Documents 4 and 5). Among them, multi-walled carbon nanotubes having an outer diameter of 10 nm to several tens of nm are relatively inexpensive and are expected to be put into practical use.

When carbon nanotubes are used, a conductive network can be efficiently formed with a small amount, and the amount of conductive material contained in the positive electrode and the negative electrode for a lithium ion secondary battery can be reduced. However, since carbon nanotubes have a very strong cohesive force and are difficult to disperse, it has not been possible to obtain a carbon nanotube dispersion composition having sufficient dispersibility.

Therefore, a method for obtaining a carbon nanotube dispersion composition by various production methods has been proposed. For example, Patent Document 6 proposes a method of producing a carbon nanotube dispersion liquid having a high concentration and high conductivity by charging multi-walled carbon nanotubes in multiple stages and performing dispersion treatment using a bead mill.

Further, Patent Document 7 proposes a method for producing a carbon nanotube dispersion having a high concentration and a low viscosity by dispersing carbon nanotubes in multiple steps using a high-pressure homogenizer, but the treatment amount is low. , There was a problem in productivity.

Therefore, a method for producing a carbon nanotube dispersion composition having high concentration, low viscosity, high conductivity, and high productivity has been an important issue for expanding applications.

Japanese Unexamined Patent Publication No. 4-155776 Japanese Unexamined Patent Publication No. 4-237971 Japanese Unexamined Patent Publication No. 2004-178922 Japanese Unexamined Patent Publication No. 2011-070908 Japanese Unexamined Patent Publication No. 2005-162877 Patent No. 5604609 Patent No. 6054296

An object to be solved by the present invention is to provide a method for producing a carbon nanotube dispersion composition having excellent conductivity and high productivity.

As a result of diligent studies in order to solve the above problems, the present inventor has used a bead mill for a method for producing a carbon nanotube dispersion composition for a battery containing carbon nanotubes, a dispersant, and an aqueous liquid medium. Including the step (step A) of performing the dispersion treatment, the carbon nanotubes are continuously or discontinuously added until the concentration of the carbon nanotube dispersion composition for batteries reaches a target value, and the carbon nanotubes are added. Before or at the same time as the addition, the dispersant is added, and the diameter of the beads of the bead mill is in the range of 0.01 to 1.25 mm, and further, for the battery obtained in step A. By including a step (step B) of dispersing the carbon nanotube dispersion composition (A) using a high-pressure homogenizer and using a hydride nitrile butadiene rubber as the dispersant, the carbon nanotube dispersion composition is excellent in conductivity and We have found a method for producing a carbon nanotube dispersion composition having high productivity, and have arrived at the present invention.

That is, the present invention is a method for producing a carbon nanotube dispersion composition for batteries, which comprises carbon nanotubes, a dispersant, and an aqueous liquid medium, and includes a step (step A) of performing a dispersion treatment using a bead mill. The step of performing the dispersion treatment (step A) is a step of continuously or discontinuously adding the carbon nanotubes to the dispersion until the carbon nanotube concentration in the carbon nanotube dispersion composition for a battery reaches a target value. (Step A1) and a step (step A2) of adding the dispersant to the dispersion before adding the carbon nanotubes or at the same time as the step A1 are included, and the diameter of the beads of the bead mill is 0.01 to 0.01 to The present invention relates to a method for producing a carbon nanotube dispersion composition for a battery, which comprises a range of 1.25 mm.

The present invention further comprises a step (step B) of dispersing the carbon nanotube dispersion composition (A) for a battery obtained in the step A using a high-pressure homogenizer (step B). The present invention relates to a method for producing a carbon nanotube dispersion composition.

The present invention is also characterized in that the viscosity of the carbon nanotube dispersion composition (A) for a battery obtained in step A at 60 rpm in a B-type viscometer is in the range of 500 to 8000 mPa · s. The present invention relates to a method for producing a carbon nanotube dispersion composition.

The present invention also relates to the above-mentioned production method, wherein the dispersant contains a hydrogenated nitrile butadiene rubber.

According to the method for producing a carbon nanotube dispersion composition of the present invention, the carbon nanotube can be dispersed without being crushed or damaged more than necessary, and high conductivity can be exhibited. In addition, it is possible to increase the productivity of the dispersion composition. As a result, for example, when used as a conductive material in a lithium ion secondary battery, a homogeneous conductive network of carbon nanotubes can be formed, and an electrode film having high conductivity and adhesion can be obtained, and thus the rate. It is possible to manufacture a non-aqueous electrolyte secondary battery having excellent characteristics and cycle characteristics.

Hereinafter, the method for producing the carbon nanotube dispersion composition for batteries of the present invention will be described in detail.

<Carbon nanotube dispersion composition for batteries>
The carbon nanotube dispersion composition for batteries of the present embodiment is characterized by containing at least carbon nanotubes, a dispersant, and an aqueous liquid medium.

<Carbon nanotube>
The carbon nanotube of this embodiment has a shape in which flat graphite is wound into a cylindrical shape. The carbon nanotubes may be a mixture of single-walled carbon nanotubes. Single-walled carbon nanotubes have a structure in which one layer of graphite is wound. Multi-walled carbon nanotubes have a structure in which two or three or more layers of graphite are wound. Further, the side wall of the carbon nanotube does not have to have a graphite structure. For example, a carbon nanotube having a side wall having an amorphous structure can be used as the carbon nanotube.

The shape of the carbon nanotubes of this embodiment is not limited. Such shapes include various shapes including needle shape, cylindrical tube shape, fish bone shape (fishbone or cup laminated type), playing card shape (platelet) and coil shape. In the present embodiment, the shape of the carbon nanotubes is preferably needle-shaped or cylindrical tube-shaped. The carbon nanotubes may have a single shape or a combination of two or more shapes.

The form of the carbon nanotubes of the present embodiment includes, but is not limited to, for example, graphite whisker, firamentas carbon, graphite fiber, ultrafine carbon tube, carbon tube, carbon fibril, carbon microtube and carbon nanofiber. .. The carbon nanotubes may have a single form thereof or a combination of two or more kinds thereof.

BET specific surface area of the carbon nanotubes of the present embodiment is preferably from 20~1000m ² / g, more preferably 150~800m ² / g.

The outer diameter of the carbon nanotubes of the present embodiment is preferably 1 to 30 nm, more preferably 1 to 20 nm.

The carbon purity of the carbon nanotubes of the present embodiment is represented by the content (mass%) of carbon atoms in the conductive material. The carbon purity is preferably 90% by mass, more preferably 95% by mass or more, still more preferably 98% by mass or more, based on 100% by mass of the conductive material.

The volume resistivity of the carbon nanotubes of the present embodiment is preferably 1.0 × 10 ^{-3 to} 1.0 × 10 ^-1 Ω · cm, and 1.0 × 10 ^{-3 to} 1.0 × 10 ^-2. It is more preferably Ω · cm. The volume resistivity of the conductive material can be measured using a powder resistivity measuring device (manufactured by Mitsubishi Chemical Analytech Co., Ltd .: Lorester GP powder resistivity measuring system MCP-PD-51)).

<Dispersant>
The dispersant of the present embodiment is not particularly limited, and can be used alone or in combination of two or more regardless of whether it is a commercially available product or a synthetic product. By dispersing the carbon nanotubes with a dispersant, a carbon nanotube dispersion composition having a higher concentration and good storage stability can be obtained.

As the dispersant that functions in the aqueous liquid medium, for example, polyvinylpyrrolidone, polyvinyl acetal, polyvinyl alcohol, or the like can be used. In particular, as a dispersant that functions suitably in an N-methyl-2-pyrrolidone (NMP) solvent, in addition to the above, a partially or entirely hydrogenated nitrile butadiene rubber, JP-A-2009-026744 and WO2008- The organic dye derivative and triazine derivative described in 108360A can be used.

Specifically, the hydrogenated nitrile butadiene-based rubber contains a hydrogenated conjugated diene-derived structural unit, an α, β-unsaturated nitrile-derived structural unit, and a conjugated diene-derived structural unit, based on the total weight of the rubber. , The hydrogenated conjugated diene-derived structural unit may be contained in an amount of 20% to 80% by weight. When it is contained in the above-mentioned content, the miscibility with NMP is increased, and the dispersibility of carbon nanotubes can be enhanced.

When the dispersant is used in the present embodiment, the carbon nanotubes can be uniformly dispersed in the aqueous liquid medium by adding a sufficient amount of the dispersant. When the amount of carbon nanotubes contained in the carbon nanotube dispersion composition is 100 parts by mass, the total amount of the dispersant used for the dispersion treatment of carbon nanotubes is preferably 1 part by mass or more and 40 parts by mass or less. By blending the dispersant in this amount ratio, it is possible to exhibit the good conductivity of the present embodiment. The dispersant is a non-conductive component, and when considered for use in a lithium ion secondary battery, it generally has low electrochemical stability and resistance to a non-aqueous electrolyte solution. Therefore, when the compounding ratio of the dispersant is 40 parts by mass or more, even if the initial characteristics are good, the characteristics may deteriorate over time. The compounding ratio of the dispersant is preferably as small as possible within the range in which the carbon nanotubes can be preferably dispersed.

<Aqueous liquid medium>
The aqueous liquid medium of the present embodiment is not particularly limited as long as the carbon nanotubes can be dispersed, but may be a mixed solvent composed of water and / or a water-soluble organic solvent. preferable.

As the aqueous liquid medium, alcohol-based (methanol, ethanol, propanol, isopropanol, butanol, isobutanol, secondary butanol, tertiary butanol, benzyl alcohol, etc.) and polyhydric alcohol-based (ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, etc.) , Propylene glycol, dipropylene glycol, polypropylene glycol, butylene glycol, hexanediol, pentanediol, glycerin, hexanetriol, thiodiglycol, etc., polyhydric alcohol ethers (ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol) Monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl 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, etc.), amine-based (ethanolamine, diethanolamine, triethanolamine, N-methyldiethanolamine, N-ethyldiethanolamine, morpholine, N-ethylmorpholine, Ethylenediamine, diethylenediamine, triethylenetetramine, tetraethylenepentamine, polyethyleneimine, pentamethyldiethylenetriamine, tetramethylpropylenediamine, etc.), amides (N-methyl-2-pyrrolidone (NMP), N-ethyl-2-pyrrolidone (N-ethyl-2-pyrrolidone) NEP), N, N-dimethylformamide, N, N-dimethylacetamide, N, N-diethylacetamide, N-methylcaprolactam, etc.), heterocyclic system (cyclohexylpyrrolidone, 2-oxazolidone, 1,3-dimethyl-2- Imidazolidinone, γ-butyrolactone, etc.), sulfoxides (dimethylsulfoxide, etc.), sulfones (hexamethylphosphorotriamide, sulfolane, etc.), lower ketones (acetone, methylethylketone, etc.), and others, tetrahydrofuran, urea, acetoni, etc. Trills and the like can be used. Of these, water or an amide-based organic solvent is more preferable, and N-methyl-2-pyrrolidone and N-ethyl-2-pyrrolidone are particularly preferable among the amide-based organic solvents.

The solid content (concentration) of the carbon nanotubes of the present embodiment is preferably 0.05 to 20% by mass, more preferably 0.1 to 10% by mass, based on 100% by mass of the carbon nanotube dispersion composition.

<Bead mill>
The bead mill of this embodiment includes a paint conditioner (manufactured by Red Devil), a ball mill, a sand mill ("Dyno Mill" manufactured by Simmal Enterprises, etc.), an attritor, a pearl mill ("DCP mill" manufactured by Eirich, etc.), or a coball mill. However, the media type disperser such as the above can be used, but the present invention is not limited thereto. Further, it is preferable to use a device that has been subjected to metal contamination prevention treatment from the apparatus, such as a method in which the agitator and the vessel use a bead mill made of ceramic or resin, or the surface of the metal agitator and vessel is sprayed with tungsten carbide or resin coated. It is preferable to use a bead mill subjected to the above treatment. As the medium, it is preferable to use glass beads, zirconia beads, or ceramic beads such as alumina beads. Only one type of bead mill may be used, or a plurality of types of devices may be used in combination.

<Bead diameter (size)>
In the dispersion treatment with the bead mill, the influence of the bead diameter (size) is large. As the bead diameter increases, the mass of the beads also increases in proportion to the cube root, so that the crushing force exerted by the beads on the carbon nanotubes increases.
In general, the initial carbon nanotube agglomerates are loosened and crushed and damaged at the same time by the dispersion treatment with the bead mill. Therefore, if the appropriate bead size (diameter) is not selected, the dispersion treatment with the bead mill is performed. Later, even if the viscosity of the obtained carbon nanotube dispersion composition is the same, the carbon nanotubes are more crushed and damaged, and the subsequent effects such as deterioration of conductivity in the lithium ion secondary battery appear.
In the present embodiment, the diameter (size) of the beads is preferably in the range of 0.01 to 1.25 mm, more preferably in the range of 0.01 to 1.0 mm. By setting the diameter (size) of the beads within this range, the carbon nanotubes are loosened, crushing and damage are reduced, and the dispersion treatment proceeds effectively.

<Manufacturing method of dispersion composition>
According to the present embodiment, the carbon nanotubes and the dispersant are simultaneously and continuously charged into the bead mill in several stages with respect to the predetermined carbon nanotube target concentration, and the dispersion treatment is performed. Then, the dispersion treatment by the bead mill is continued until the carbon nanotube dispersion composition obtained at each step has a sufficiently low viscosity and good fluidity is obtained. When the carbon nanotube dispersion composition obtained in each step is in the above-mentioned state, the carbon nanotubes and the dispersant are again simultaneously and continuously charged into the bead mill, and the process is repeated until a predetermined carbon nanotube target concentration is reached.

The ratio of the dispersant to the carbon nanotubes is preferably set to a preset ratio. As a result, it is possible to prevent the dispersant from being non-uniformly adsorbed on the carbon nanotubes, which makes the dispersion treatment difficult. When the adsorption of the dispersant on the carbon nanotubes becomes non-uniform, the viscosity of the dispersion composition during the dispersion treatment rapidly increases, and the amount of energy input for advancing the dispersion treatment increases. As a result, the crushing and damage of the carbon nanotubes inevitably become large, which causes deterioration of conductivity and the like. In addition, the non-uniformity of the dispersant adsorption on the carbon nanotubes also deteriorates the storage stability of the dispersion composition.

According to the present embodiment, the adsorption of the dispersant on the carbon nanotubes becomes more uniform, the viscosity of the dispersion composition can be prevented from rapidly increasing during the dispersion treatment, and the amount of energy input in the dispersion treatment can be reduced. In addition, since the carbon nanotubes can be dispersed without being crushed or damaged more than necessary, the carbon nanotube dispersion composition for batteries has good conductivity and storage stability, and is also superior in terms of productivity. It is a manufacturing method.

<High pressure homogenizer>
As the high-pressure homogenizer in the present embodiment, wet jet mills such as "Genus PY" manufactured by Genus, "Starburst" manufactured by Sugino Machine, and "Nammizer" manufactured by Nanomizer can be used, but are limited thereto. It's not a thing. The high pressure homogenizer includes a pump and one or more nozzles, and there are various nozzle shapes for performing dispersion processing.
For example, there are a type in which raw materials collide with each other at high pressure, a type in which high pressure raw materials collide with a ceramic ball, a type in which a high pressure raw material is passed through a slit and processed by the shearing force, and a type in which cavitation by a jet of high pressure raw materials is used. It is not limited.

The diameter of the nozzle can be changed according to the dispersion processing step. In the initial stage where the dispersion treatment has not yet progressed, it is preferable to use a nozzle having a diameter larger than that of the maximally aggregated carbon nanotubes in order to prevent its blockage. On the other hand, if the nozzle diameter is large, the amount of energy input is reduced, so that the productivity may be deteriorated.

The pressure used in the high pressure homogenizer is generally 70-250 MPa.

According to the present embodiment, the carbon nanotube dispersion composition for batteries containing carbon nanotubes, a dispersant, and an aqueous liquid medium is subjected to a dispersion treatment step (step A) by a bead mill, and further dispersed by a high-pressure homogenizer (step). Perform B). This makes it possible to proceed with the dispersion treatment without crushing and damaging the carbon nanotubes more than necessary. Therefore, after the dispersion treatment in step A, the remaining bundled carbon nanotubes and their aggregates in the obtained carbon nanotube dispersion composition (A) become shorter than necessary through step B. It is loosened and the proportion of long carbon nanotubes increases. As a result, a carbon nanotube dispersion composition having good conductivity can be obtained.

When the carbon nanotube dispersion composition (A) obtained in step A is subjected to dispersion treatment with a high-pressure homogenizer, the dispersion composition (A) should have a lower viscosity and less agglomerates in order to prevent clogging of the nozzles used. preferable. Specifically, the viscosity of the dispersion composition (A) at 60 rpm in the B-type viscometer is preferably in the range of 500 to 8000 mPa · s. If the viscosity is 8000 mPa · s or more, the dispersion treatment of the carbon nanotubes of the dispersion composition (A) is insufficient, and the nozzle may be clogged.

According to the present embodiment, the conductivity of the carbon nanotube dispersion composition can be easily improved by additionally dispersing the carbon nanotube dispersion composition (A) obtained through the step A in the step B. .. That is, when the dispersion treatment of carbon nanotubes is performed only with a high-pressure homogenizer to produce the dispersion composition, it is necessary to carry out the dispersion treatment in a state of low viscosity and less agglomerates in order not to block the nozzles, which is inevitable. The amount of carbon nanotubes and dispersants used is limited. Therefore, it takes a large amount of production time to reach a predetermined target carbon nanotube concentration.
Since the carbon nanotube dispersion composition (A) obtained through the step A has a sufficiently low viscosity and a small amount of agglomerates, it is possible to carry out the additional dispersion treatment according to the subsequent step B without blocking the nozzles. Further, also in the step B, the dispersion treatment can proceed more efficiently, and the conductivity of the carbon nanotube dispersion composition can be improved.

The carbon nanotube dispersion composition obtained by the present embodiment can be suitably used for a lithium ion secondary battery.

<Carbon nanotube-containing resin composition>
The carbon nanotube-containing resin composition in the present embodiment further contains at least a binder resin in the carbon nanotube dispersion composition.

<Binder resin>
The binder resin in this embodiment is a resin for binding substances.

Examples of the binder resin of the present embodiment include ethylene, propylene, vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acrylic acid, acrylic acid ester, methacrylic acid, methacrylic acid ester, acrylonitrile, styrene, vinyl butyral, and vinyl acetal. , Vinyl pyroridone, etc. as a constituent unit; polyurethane resin, polyester resin, phenol resin, epoxy resin, phenoxy resin, urea resin, melamine resin, alkyd resin, acrylic resin, formaldehyde resin, silicon resin, fluorine Resins; cellulose resins such as carboxymethyl cellulose; rubbers such as styrene butadiene rubber and fluororubber; conductive resins such as polyaniline and polyacetylene. Further, modified products and mixtures of these resins and copolymers may be used. Among them, when used as a binder resin for a positive electrode, it is preferable to use a polymer compound having a fluorine atom in the molecule from the viewpoint of resistance, for example, polyvinylidene fluoride, polyvinyl fluoride, tetrafluoroethylene and the like. When used as a binder resin for the negative electrode, carboxymethyl cellulose, styrene butadiene rubber, and polyacrylic acid having good adhesion are preferable.

The weight average molecular weight of these resins as the binder resin of the present embodiment is preferably 10,000 to 2,000,000, more preferably 100,000 to 1,000,000, and 200,000 to 1,000. 000 is particularly preferred.

<Mixed material slurry>
The mixture slurry of the present embodiment further contains at least an active material in the carbon nanotube-containing resin composition.

<Active material>
The active material of the present embodiment is a material that is the basis of a battery reaction. The active material is divided into a positive electrode active material and a negative electrode active material according to the electromotive force.

The positive electrode active material is not particularly limited, but a metal oxide capable of doping or intercalating lithium ions, a metal compound such as a metal sulfide, a conductive polymer, or the like can be used. Examples thereof include oxides of transition metals such as Fe, Co, Ni and Mn, composite oxides with lithium, and inorganic compounds such as transition metal sulfides. Specifically, transition metal oxide powders such as MnO, V ₂ O ₅ , V ₆ O ₁₃ , TiO ₂ , layered lithium nickelate, lithium cobaltate, lithium manganate, lithium manganate with spinel structure, etc. Examples thereof include a composite oxide powder of lithium and a transition metal, a lithium iron phosphate-based material which is a phosphoric acid compound having an olivine structure, and a transition metal sulfide powder such as TiS ₂ and FeS. Further, a conductive polymer such as polyaniline, polyacetylene, polypyrrole, or polythiophene can also be used. Further, the above-mentioned inorganic compounds and organic compounds may be mixed and used.

The negative electrode active material is not particularly limited as long as it can be doped with or intercalated with lithium ions. For example, metal Li, alloys such as tin alloys, silicon alloys, and lead alloys, Li _X Fe ₂ O ₃ , Li _X Fe ₃ O ₄ , and Li _X WO ₂ (x is a number of 0 <x <1). ), Metal oxides such as lithium titanate, lithium vanadium, lithium siliconate, conductive polymer such as polyacetylene and poly-p-phenylene, amorphous carbonaceous materials such as soft carbon and hard carbon. Examples thereof include artificial graphite such as highly graphitized carbon material, carbonaceous powder such as natural graphite, carbon black, mesophase carbon black, resin-fired carbon material, vapor-grown carbon fiber, and carbon-based material such as carbon fiber. These negative electrode active materials may be used alone or in combination of two or more.

The mixture slurry of the present embodiment can be produced by various conventionally known methods. For example, a method of adding an active material to the carbon nanotube dispersion composition and then adding a binder resin to prepare the carbon nanotube dispersion composition, or a method of mixing the carbon nanotube dispersion composition and the binder resin and then adding the active material can be mentioned.

In order to obtain the mixture slurry of the present embodiment, it is preferable to add an active material to the carbon nanotube dispersion composition and then carry out a dispersion treatment. The disperser used to perform such processing is not particularly limited.

<Electrode film>
The electrode film of the present embodiment is formed by forming a mixture slurry in the form of a film. For example, it is a coating film in which an electrode mixture layer is formed by applying and drying a mixture slurry on a current collector.

The material and shape of the current collector used for the electrode film of the present embodiment are not particularly limited, and those suitable for various secondary batteries can be appropriately selected. For example, examples of the material of the current collector include metals and alloys such as aluminum, copper, nickel, titanium, and stainless steel. As the shape, a foil on a flat plate is generally used, but a roughened surface, a perforated foil, or a mesh-shaped current collector can also be used.

The method of applying the mixture slurry on the current collector is not particularly limited, and a known method can be used. Specific examples include a die coating method, a dip coating method, a roll coating method, a doctor coating method, a knife coating method, a spray coating method, a gravure coating method, a screen printing method or an electrostatic coating method, and drying. As the method, a neglected drying, a blower dryer, a warm air dryer, an infrared heater, a far infrared heater and the like can be used, but the method is not particularly limited thereto.

Further, after coating, a rolling process such as a lithographic press or a calendar roll may be performed. The thickness of the electrode mixture layer is generally 1 μm or more and 500 μm or less, preferably 10 μm or more and 300 μm or less.

<Non-aqueous electrolyte secondary battery>
The non-aqueous electrolyte secondary battery of the present embodiment includes a positive electrode, a negative electrode, and an electrolyte.

As the positive electrode, a current collector obtained by applying and drying a mixture slurry containing a positive electrode active material to prepare an electrode film can be used.

As the negative electrode, a mixture slurry containing the negative electrode active material on the current collector is coated and dried to prepare an electrode film.

As the electrolyte, various conventionally known electrolytes in which ions can move can be used. For example, 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 (where Ph is a phenyl group) and the like, but are not limited thereto. The electrolyte is preferably dissolved in a non-aqueous solvent and used as an electrolytic solution.

The non-aqueous solvent is not particularly limited, and is, for example, carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, ethylmethyl carbonate, and diethyl carbonate; γ-butylolactone, γ-valerolactone, and γ. -Lactones such as octanoic lactones; tetrahydrofuran, 2-methyltetraethane, 1,3-dioxolane, 4-methyl-1,3-dioxolane, 1,2-methoxyethane, 1,2-ethoxyethane, and 1, Glymes such as 2-dibutoxyethane; esters such as methylformates, methylacetates, and methylpropionates; sulfoxides such as dimethylsulfoxide and sulfolanes; and nitriles such as acetonitrile. Each of these solvents may be used alone, or two or more kinds may be mixed and used.

The non-aqueous electrolyte secondary battery of the present embodiment preferably contains a separator. Examples of the separator include polyethylene non-woven fabric, polypropylene non-woven fabric, polyamide non-woven fabric, and those obtained by subjecting them to a hydrophilic treatment, but the separator is not particularly limited thereto.

The structure of the non-aqueous electrolyte secondary battery of the present embodiment is not particularly limited, but is usually composed of a positive electrode and a negative electrode, and a separator provided as needed, such as a paper type, a cylindrical type, a button type, and a laminated type. It can have various shapes according to the purpose of use.

Hereinafter, the present invention will be described in more detail with reference to examples. The present invention is not limited to the following examples as long as the gist of the present invention is not exceeded. In the examples, "carbon nanotubes" may be abbreviated as "CNT". Unless otherwise specified, "parts" represents "parts by mass" and "%" represents "% by mass".

<Viscosity measurement of carbon nanotube dispersion composition>
To measure the viscosity value, use a B-type viscometer (“BL” manufactured by Toki Sangyo Co., Ltd.), stir the dispersion with a spatula at a dispersion temperature of 25 ° C, and then rotate the rotor of the B-type viscometer. Immediately at 60 rpm. When the viscosity value of the rotor used for the measurement was less than 100 mPa · s, No. If 1 is 100 or more and less than 500 mPa · s, No. If 2 is 500 or more and less than 2000 mPa · s, No. If 3 is 2000 or more and less than 10000 mPa · s, No. Each of 4 was used. Generally, the lower the viscosity, the better the dispersibility, and the higher the viscosity, the poorer the dispersibility.

<Preparation of carbon nanotube dispersion composition>
(Example 1-A)
A carbon nanotube dispersion composition was prepared by setting the final target concentration of CNT to 6% and the amount of dispersant to 25% with respect to CNT, and adding CNT in 5 steps. The procedure is as follows.

First, 64 parts of NMP was put into a stainless steel container, and while stirring with a disper, a pre-prepared hydrogenated butadiene rubber Therban (registered trademark) 4637 (manufactured by LANXESS, solid content 100%, acrylonitrile content 43) was prepared as a dispersant. %) 5% NMP solution (containing 0.3 parts of hydrogenated butadiene rubber as a dispersant; 1/5 of the total amount of dispersant) and JENOTUBE8S (manufactured by JEIO, multilayer) as carbon nanotubes. 1.2 parts (1/5 of the total amount of CNT) of CNT (outer diameter 6 to 9 nm) were charged simultaneously and continuously. The addition of the CNT and the dispersant solution was adjusted so that these ratios were as constant as possible.
Next, the contents in the stainless steel container were sent by a tube pump, and dispersion treatment was performed by a bead mill (Dynomill MULTI LAB, manufactured by Simmal Enterprises) filled with zirconia beads having a diameter of 1.00 mm. The contents obtained by the dispersion treatment are discharged into the stainless steel container again by the tube pump, and the viscosity is lowered by the continuous dispersion treatment.
After confirming that the viscosity of the contents in the stainless steel container has decreased and that the contents have sufficient fluidity, 1.2 parts of CNT (JENOTUBE8S), which is the second stage, and a dispersant solution (5 of hydrogenated butadiene rubber) % NMP solution) 6 parts were added in the same manner as above.
The above-mentioned divided addition of the CNT and the dispersant was repeated up to the fifth step, and the dispersion treatment was continuously carried out to obtain a carbon nanotube dispersion composition having a low viscosity and sufficient fluidity. The viscosity of the obtained carbon nanotube dispersion composition was 2500 mPa · s at 60 rpm of the B-type viscometer.

(Example 1-A; Preparation of mixture slurry)
Positive electrode active material (BASF Toda Battery Materials GK, NCA NAT-7150) 98.4 parts by mass, 11.7 parts by mass of the carbon nanotube dispersion composition, PVDF (Solvay, Solef (registered trademark) # 5130) It was added to a plastic container having a capacity of 150 cm ³ of 8% NMP solution 12.5 parts by mass and mixed until the powder is homogeneous with a spatula. Then, using a rotation / revolution mixer (Awatori Rentaro manufactured by Shinky Co., Ltd., ARE-310), the mixture was stirred at 2000 rpm for 30 seconds. Then, the mixture in the plastic container was mixed using a spatula until uniform, and the mixture was stirred again at 2000 rpm for 2 minutes using a rotation / revolution mixer. Next, 5.6 parts by mass of NMP was added, and the mixture was stirred at 2000 rpm for 30 seconds using a rotation / revolution mixer to obtain a mixture slurry.

(Example 1-A; Measurement of volume resistivity of composite coating film)
The above-mentioned mixture slurry is applied onto PET foil using an applicator so that the basis weight per unit of the electrodes is 20 mg / cm ^2, and then applied in an electric oven at 120 ° C. ± 5 ° C. for 25 minutes. The membrane was dried. Then, the surface resistivity (Ω / □) of the coating film after drying was measured using Lorester GP and MCP-T610 manufactured by Mitsubishi Chemical Analytech Co., Ltd. After the measurement, the thickness of the electrode mixture layer formed on the PET foil was multiplied to obtain the volume resistivity (Ω · cm) of the electrode film for the positive electrode. The thickness of the electrode mixture layer was calculated by subtracting the film thickness of the PET foil from the average value measured at three points in the electrode film using a film thickness meter (DIGIMICRO MH-15M manufactured by NIKON).
The results are shown in Table 1.
The volume resistivity of the mixture coating film is preferably 15 Ω · cm or less, and more preferably 10 Ω · cm or less.

・ 8S: JENOTUBE8S (manufactured by JEIO, multi-walled CNT, outer diameter 6-9 nm)
HNBR: Therban (registered trademark) 4637 (manufactured by LANXESS, solid content 100%, acrylonitrile content 43%)
・ NMP: N-methyl-2-pyrrolidone

(Comparative Example 1-A)
The final target concentration of CNT was set to 6%, the amount of dispersant was set to 25% with respect to CNT, and a carbon nanotube dispersion composition was prepared by adding the entire amount of CNT in one step. The procedure is as follows.
First, 64 parts of NMP was put into a stainless steel container, and 30 parts of a 5% NMP solution of a pre-prepared hydrogenated butadiene rubber Therban (registered trademark) 4637 (1 hydrogenated butadiene rubber as a dispersant) was put into a stainless steel container. After adding 5 parts), 6 parts of JENOTUBE8S were continuously added as carbon nanotubes while stirring with a disperser.
Next, the contents in the stainless steel container were sent by a tube pump, and dispersion treatment was performed by a bead mill (Dynomill MULTI LAB, manufactured by Simmal Enterprises) filled with zirconia beads having a diameter of 1.00 mm. The contents obtained by the dispersion treatment are discharged into the stainless steel container again by the tube pump, and the viscosity is lowered by the continuous dispersion treatment.
The dispersion treatment was continuously continued with a bead mill until the viscosity of the contents in the stainless steel container reached 2500 mPa · s at 60 rpm of the B-type viscometer to obtain a carbon nanotube dispersion composition. When the volume resistivity of the mixture coating film was measured using the obtained carbon nanotube dispersion composition in the same manner as described above, it was 38Ω · cm.

(Comparative Example 2-A)
The dispersion treatment was carried out in the same manner as in Example 1-A except that the diameter of the beads in the dispersion step using the bead mill was 1.5 mm, and the viscosity of the obtained carbon nanotube dispersion composition was 2500 mPa · at 60 rpm of the B-type viscometer. Continued until s. When the volume resistivity of the mixture coating film was measured using the obtained carbon nanotube dispersion composition in the same manner as described above, it was 23 Ω · cm.

(Comparative Example 3-A)
The dispersion treatment was carried out in the same manner as in Example 1-A except that the diameter of the beads in the dispersion step using the bead mill was 1.5 mm, and the viscosity of the obtained carbon nanotube dispersion composition was 9000 mPa · at 60 rpm of the B-type viscometer. Continued until s. Using the obtained carbon nanotube dispersion composition, the volume resistivity of the mixture coating film was measured in the same manner as above and found to be 530 Ω · cm.

From the above results, the conductivity of the obtained carbon nanotube dispersion composition was changed depending on the conditions of the dispersion treatment (step A) by the bead mill. On the other hand, as confirmed in Comparative Example 1-A, when the dispersion treatment (step A) by the bead mill was not performed in multiple steps, the conductivity was significantly deteriorated. It is considered that this is because the adsorption of the dispersant to the CNTs became non-uniform and the processing viscosity in the bead mill became high, so that excess energy was given to the CNTs, and as a result, the CNTs were crushed or damaged. Further, as confirmed in Comparative Example 2-A, even when the bead diameter is 1.5 mm, it is considered that the CNT is crushed or damaged in the same manner as described above due to the increase in the impact force of the beads. .. Further, as confirmed in Comparative Example 3-A, in order to suppress crushing and damage of CNTs, the conductivity of the carbon nanotube dispersion composition even when the dispersion treatment is terminated when the viscosity is not sufficiently lowered. Has deteriorated significantly. It is considered that this is because CNTs remain as agglomerates in the first place.
From the above, it has been clarified that the present invention can provide a carbon nanotube dispersion composition for a battery having high conductivity, which is difficult to realize by a conventional method for producing a carbon nanotube dispersion composition for a battery.

(Example 1-B)
The carbon nanotube dispersion composition obtained in Example 1-A was subjected to additional dispersion treatment with a high-pressure homogenizer (Starburst 10, manufactured by Sugino Machine Limited). A two-pass treatment was performed using a single nozzle chamber with a nozzle diameter of 0.12 mm and a pressure of 150 MPa. The viscosity of the obtained carbon nanotube dispersion composition was 900 mPa · s at 60 rpm of the B-type viscometer. Further, when the volume resistivity of the mixture coating film was measured in the same manner as described above, it was 6Ω · cm.

(Comparative Examples 1-B and 2-B)
The additional dispersion treatment with a high-pressure homogenizer (Starburst 10, manufactured by Sugino Machine Limited) was carried out in the same manner as in Example 1-B except that the carbon nanotube dispersion compositions obtained in Comparative Examples 1-A and 2-A were used. A carbon nanotube dispersion composition was obtained. The results are shown in Table 2.

(Comparative Example 3-B)
The additional dispersion treatment with a high-pressure homogenizer (Starburst 10, manufactured by Sugino Machine Limited) was carried out in the same manner as in Example 1-B except that the carbon nanotube dispersion composition obtained in 3-A was used. Immediately after the composition was charged, the nozzle was blocked, and subsequent dispersion treatment was difficult.

(Comparative Example 4)
The final target concentration of CNT is set to 6 parts, the dispersant is set to 1.5 parts (25% of CNT ratio), and NMP is set to 92.5 parts, and the carbon nanotube dispersion composition is prepared only with a high-pressure homogenizer (Starburst 10, manufactured by Sugino Machine Limited). Made. The procedure is as follows.
First, 64 parts of NMP was put into a stainless steel container, and while stirring with a disper, a pre-prepared hydride-based rubber, Theban (trademark registration) 4637 (manufactured by LANXESS, solid content 100%, acrylonitrile content 43) was prepared as a dispersant. %) Of 5% NMP solution (containing 0.3 parts of butadiene rubber hydride as a dispersant; 1/5 of the total amount of dispersant) and JENOTUBE8S (manufactured by JEIO) 1.2 parts of CNT (outer diameter 6 to 9 nm) (1/5 of the final target CNT concentration) were added simultaneously and continuously. The addition of the CNT and the dispersant solution was adjusted so that these ratios were as constant as possible.
Next, the contents in the stainless steel container were sent by a diaphragm pump, and dispersion treatment was performed by a high-pressure homogenizer (Starburst 10, manufactured by Sugino Machine Limited). The dispersion treatment with a high-pressure homogenizer was performed using a single nozzle chamber with a nozzle diameter of 0.15 mm and a pressure of 150 MPa. The contents obtained by the dispersion treatment are discharged into the stainless steel container again by the diaphragm pump, and the viscosity is lowered by the continuous dispersion treatment.
After confirming that the viscosity of the contents in the stainless steel container has decreased and that the contents have sufficient fluidity, 1.2 parts of CNT (JENOTUBE8S), which is the second step, and a dispersant solution (5 of hydrogenated butadiene rubber) % NMP solution) 6 parts were added in the same manner as above.
The above-mentioned divided addition of the CNT and the dispersant was repeated up to the fifth step, and when the CNT concentration reached a predetermined target value, the process was changed to the path dispersion treatment and the dispersion treatment was continued. That is, the contents in the stainless steel container were sent by a diaphragm pump, dispersed by a high-pressure homogenizer, and then discharged to another container. When all the contents in the stainless steel container have undergone dispersion treatment with a high-pressure homogenizer, they are counted as 1 pass, and the pass dispersion treatment is performed until the viscosity of the obtained carbon nanotube dispersion composition reaches 900 mPa · s at 60 rpm of a B-type viscometer. Was done. Finally, 140 pass dispersion treatments were required to reach the target viscosity. When the volume resistivity of the mixed material coating film of the obtained carbon nanotube dispersion composition was measured in the same manner as described above, it was 6Ω · cm.

From the above results, the conductivity of the carbon nanotube dispersion composition obtained by performing the dispersion treatment with a high-pressure homogenizer after the dispersion treatment with a bead mill (step A) was improved. On the other hand, as confirmed in Comparative Examples 1-B to 3-B, when the dispersion treatment (step A) by the bead mill was not performed under appropriate conditions, even if the dispersion treatment by the high-pressure homogenizer was performed, the dispersion treatment was performed. The effect is small. Further, in Comparative Example 4, all the dispersion treatment steps were carried out by a high-pressure homogenizer, and the characteristics of the obtained carbon nanotube dispersion composition were also good, but the preparation required 140 passes of dispersion treatment. It doesn't make sense in terms of industrial productivity.
From the above, it has been clarified that the present invention can provide a carbon nanotube dispersion composition for a battery having high conductivity and productivity, which cannot be realized by a conventional method for producing a carbon nanotube dispersion composition for a battery.

Although the present invention has been described above with reference to the embodiments, the present invention is not limited to the above. Various changes that can be understood by those skilled in the art can be made within the scope of the invention in the configuration and details of the invention of the present application.

Claims (4)

A method for producing a carbon nanotube dispersion composition for a battery, which comprises a carbon nanotube, a dispersant, and an aqueous liquid medium.
Including the step (step A) of performing the dispersion treatment using a bead mill,
The step (step A) of performing the dispersion treatment is
A step of continuously or discontinuously adding the carbon nanotubes to the dispersion until the carbon nanotube concentration in the carbon nanotube dispersion composition for a battery reaches a target value (step A1).
And, before adding the carbon nanotube, or at the same time as step A1, the step (step A2) of adding the dispersant to the dispersion liquid is included.
Moreover, a method for producing a carbon nanotube dispersion composition for a battery, wherein the diameter of the beads of the bead mill is in the range of 0.01 to 1.25 mm. The carbon for batteries according to claim 1, further comprising a step (step B) of dispersing the carbon nanotube dispersion composition (A) for batteries obtained in step A using a high-pressure homogenizer. A method for producing a nanotube dispersion composition. The battery according to claim 2, wherein the viscosity of the carbon nanotube dispersion composition for batteries (A) obtained in step A at 60 rpm in a B-type viscometer is in the range of 500 to 8000 mPa · s. A method for producing a carbon nanotube dispersion composition. The method for producing a carbon nanotube dispersion composition for a battery according to any one of claims 1 to 3, wherein the dispersant contains a hydrogenated nitrile butadiene rubber.