JP2020021632A - Carbon black dispersion composition and use thereof - Google Patents

Abstract

To provide: a carbon black dispersion composition, capable of maintaining and improving coating film uniformity and battery characteristics when being used as a mixture composition and an electrode mixture layer, while ensuring the dispersion stability of the carbon black dispersion composition.SOLUTION: A carbon black dispersion composition contains carbon black, a dispersant, and N-methyl-2-pyrrolidone. The content of carbon black is 20.5-30 mass%, and the content of the dispersant is 0.4 pt.mass or more and 20 pts.mass or less with respect to 100 pts.mass of carbon black. The dispersant is at least one selected from the group consisting of methyl cellulose and ethyl cellulose, and the shear rate showing the minimum value of viscosity is more than 1,000 s.SELECTED DRAWING: None

Description

  The present invention relates to a carbon black dispersion composition having excellent dispersibility, conductivity, and storage stability. The invention also relates to a battery electrode mixture layer and a lithium ion secondary battery using the dispersion composition.

  In the field of batteries, carbon materials are widely used as conductive aids.However, in order to make the production process more efficient and shorter when manufacturing electrodes, it is necessary to disperse the carbon material in a solvent at a high concentration and evenly. It is important to be able to apply easily.

  In recent years, in consideration of the environment and production costs in particular, by preparing a carbon material dispersion composition with a higher concentration and uniform dispersion than before, it is possible to reduce the amount of solvent used and reduce the energy used during drying. Reduction is required. These requirements have a large effect on the cost of the solvent and the energy used during drying, and therefore become more important as the solvent used is more expensive or as the solvent used has a higher boiling point.

  Lithium ion secondary batteries are widely used in automobiles and the like, and the need for higher capacity is increasing more and more. Methods for increasing the capacity include increasing the amount of active material in the coating film and reducing the amount of binder. However, an increase in the content of the active material means that the content of the conductive aid relatively decreases. At this time, if the dispersion of the conductive aid is not uniform and stable, the conductive aid and the active material are coated. It cannot be uniformly distributed on the film, which adversely affects battery characteristics. That is, the difficulty of maintaining the state of the battery electrode plate uniform and normal increases in proportion to the increase in the active material content.

  Generally, when dispersing carbon black using a dispersant, the dispersibility of carbon black deteriorates when the amount of the dispersant becomes extremely small, and conversely, the dispersibility becomes good when the amount of the dispersant becomes extremely large. However, when used in battery applications, adverse effects on battery characteristics such as an increase in resistance and deterioration in conductivity are expected. In addition, it is known that the stability of the dispersion composition and the coating film properties of the mixture composition largely depend on the dispersant to be used, but these properties are greatly improved without changing the dispersant to be used. It is generally difficult to do.

  Also, it is known that the effect of the dispersant may vary greatly depending on factors such as pH, ionic strength, and materials contained therein. Function, stability, and coating film properties may be deteriorated.

  For example, Patent Literature 1 discloses a dispersion composition using acetylene black and a dispersion medium. Patent Document 2 discloses a dispersion composition using carbon black, a nonionic dispersant, and a dispersion medium. However, in the electrode mixture composition formed using the dispersion compositions disclosed in Patent Documents 1 and 2, the battery performance and the uniformity of the coating film are insufficient. Since the conductive assistant is not uniformly distributed in the mixture layer, desirable battery characteristics cannot be obtained.

  Further, Patent Document 3 discloses that storage stability and coating film properties are improved by further containing an acidic compound in a mixture composition containing carbon black, a dispersant, a binder, and an electrode active material. I have. However, the addition of an acidic compound to the mixture composition is not desirable in that it may affect the stability and uniformity of the mixture, so that a formulation design without additives is required.

WO 2014/042266 Japanese Patent No. 5628503 JP-A-2006-046188

  In view of the above circumstances, in the present invention, when used as a mixture composition and an electrode mixture layer, the uniformity of the coating film and the battery characteristics are maintained and improved while ensuring the dispersion stability of the carbon black dispersion composition. It is an object to provide a carbon black dispersion composition that can be made to act.

  The present inventors have conducted intensive studies in order to solve the above-mentioned problems, and as a result, the dispersing composition itself by using methylcellulose or ethylcellulose as a dispersant, and increasing the shear rate at which the viscosity of the dispersion composition has a minimum value to be higher than a certain value. The present inventors have found that it is possible to achieve both the dispersibility and the stability of the compound and the uniformity of the mixture composition using the same, and have accomplished the present invention.

That is, an embodiment of the present invention is a carbon black dispersion composition containing carbon black, a dispersant, and N-methyl-2-pyrrolidone, wherein the content of carbon black is 20.5 to 30% by mass, The content of the dispersant is at least 0.4 part by mass and not more than 20 parts by mass with respect to 100 parts by mass of carbon black, and the dispersant is at least one selected from the group consisting of methyl cellulose and ethyl cellulose, and has a viscosity of at least one. The present invention relates to a carbon black dispersion composition characterized by having a shear rate showing a minimum value of more than 1000 s ^-1 .

Further, embodiments of the present invention is characterized in that shear rate as the viscosity minimum value is smaller than the larger 2000s ^-1 than 1000 s ^-1, regarding the carbon black dispersion composition.

  In addition, an embodiment of the present invention relates to the carbon black dispersion composition, wherein the content of the dispersant is 1 part by mass or more and 10 parts by mass or less based on 100 parts by mass of carbon black.

  Further, an embodiment of the present invention relates to the carbon black dispersion composition further including a binder.

  Further, an embodiment of the present invention further relates to the carbon black dispersion composition containing an active material.

  Further, an embodiment of the present invention relates to an electrode having a mixture layer formed of the carbon black dispersion composition on a current collector.

  Further, an embodiment of the present invention relates to a battery including the electrode and a non-aqueous electrolyte.

  Hereinafter, details of the present invention will be described. In the present specification, “N-methyl-2-pyrrolidone” is “NMP”, “positive electrode active material or negative electrode active material” is “electrode active material” or “active material”, “carbon material containing active material and binder”. The “black dispersion composition” may be abbreviated as “carbon black mixture paste”, “mixture paste” or “mixture composition”.

<Carbon black>
As the carbon black used in the present invention, various types such as commercially available acetylene black, furnace black, hollow carbon black, channel black, thermal black, and Ketjen black can be used. In addition, carbon black subjected to ordinary oxidation treatment, carbon black subjected to graphitization treatment, carbon nanotube, carbon nanofiber, and the like can also be used.

  The oxidation treatment of carbon black is performed by treating carbon black at a high temperature in the air or by secondary treatment with nitric acid, nitrogen dioxide, ozone, etc., for example, phenol group, quinone group, carboxyl group, carbonyl group. This is a process of directly introducing (covalently bonding) such an oxygen-containing polar functional group to the surface of carbon black, and is generally performed to improve the dispersibility of carbon black.

  The average primary particle size of the carbon black used in the production of the dispersion composition is preferably 0.01 to 1 μm, as in the average primary particle size range of the carbon black used in general dispersion compositions and coatings, and particularly preferably 0 to 1 μm. 0.01 to 0.2 μm is preferable, and 0.01 to 0.1 μm is more preferable. The term “average primary particle size” as used herein refers to an arithmetic average particle size measured by an electron microscope, and the physical property values are generally used to represent physical properties of carbon black.

  BET specific surface area and pH are known as other physical properties representing the physical properties of carbon black. The BET specific surface area refers to a specific surface area (hereinafter, simply referred to as a specific surface area) measured by a BET method by nitrogen adsorption, and the specific surface area corresponds to a surface area of carbon black. The amount required also increases. The pH changes under the influence of the functional groups and the impurities contained on the surface of the carbon black.

Carbon black used in the present invention, BET specific surface area preferably has 20~1500m ² / g, more preferably a 30~1000m ² / g, particularly preferably from 30~500m ² / g.

  Commercially available carbon blacks include, for example, Toka Black # 4300, # 4400, # 4500, # 5500 (manufactured by Tokai Carbon Co., furnace black), Printex L, etc. (manufactured by Degussa, furnace black), Raven 7000, 5750, 5250, 5000 ULTRAIII, 5000ULTRA, etc., Conductex SC ULTRA, Conductex 975 ULTRA, etc., PUER BLACK100, 115, 205, etc. (Columbian, Furnace Black), # 2350, # 2400B, # 2600B, # 3050B, # 3030B, # 3030B # 3350B, # 3400B, # 5400B, etc. (furnace black, manufactured by Mitsubishi Chemical Corporation), MONARCH 1400, 1300, 900, Vulcan XC-7 R, BlackPearls2000, etc. (manufactured by Cabot Corporation, furnace black), Ensaco250G, Ensaco260G, Ensaco350G, SuperP-Li (manufactured by TIMCAL), Ketchen Black EC-300J, EC-600JD (manufactured by Lion), Denka Black, Denka Black HS Examples of graphite such as -100, FX-35 (Denka, acetylene black) and the like include natural graphite such as artificial graphite, flake graphite, massive graphite and earthy graphite, but are not limited thereto. Instead, two or more kinds may be used in combination.

  The carbon black used in the present invention is not particularly limited, but carbon black having high conductivity and industrially produced, such as acetylene black and furnace black, is preferably used.

<Dispersant>
The dispersant in the present invention is at least one polymer selected from methylcellulose and ethylcellulose.

  The weight average molecular weight of the dispersant is preferably in the range of 20,000 to 200,000, more preferably in the range of 40,000 to 150,000. Further, it is particularly preferable that the content be in the range of 40,000 or more and 100,000 or less. When a dispersant having an excessively large molecular weight is used, the viscosity of the obtained dispersion composition becomes extremely high, and the processability and the uniformity of the dispersion composition and the mixture composition using the same deteriorate. On the other hand, a dispersant having a molecular weight that is too small has poor dispersibility, and makes it difficult to produce a dispersion composition. In order to achieve both dispersibility and stability with a limited amount of dispersant, it is desirable to use a preferred range of dispersant.

<N-methyl-2-pyrrolidone>
The carbon black dispersion composition of the present invention contains N-methyl-2-pyrrolidone (NMP). NMP is used for manufacturing electrodes of lithium ion secondary batteries. In the present invention, as long as the effect of the dispersant and the battery performance are not impaired, one or more other solvents may be used in combination, but from the industrial applicability envisioned by the present invention, NMP may be used alone. Is preferred.

  In the present invention, the amount of the solid content relative to the carbon black dispersion composition is preferably 1 to 90% by mass, more preferably 40 to 85% by mass, and more preferably 55 to 85% by mass, based on 100% by mass of the carbon black dispersion composition for a battery. % By mass is more preferable, and 60 to 85% by mass is particularly preferable.

  The carbon black dispersion composition of the present invention has a carbon black content of 20.5 to 30% by mass, and methyl cellulose and ethyl cellulose as dispersants are added in an amount of 0.4 to 100 parts by mass of carbon black. It is not less than 20 parts by mass and not more than 20 parts by mass, and further contains NMP.

  In the present invention, the addition amount of methyl cellulose and ethyl cellulose as a dispersant to carbon black is 0.4 parts by mass or more and 20 parts by mass or less, and 1 part by mass or more and 10 parts by mass with respect to 100 parts by mass of carbon black. The content is preferably 1 part by mass or more and 6 parts by mass or less.

  The amount of the dispersant added to the carbon black dispersion composition is determined by the specific surface area of the carbon black to be added, the average particle diameter of the carbon black particles after dispersion, the amount of carbon black adsorbed, and the like.

As described above, the carbon black dispersion composition of the present invention, in addition to containing a specific concentration range of carbon black and a specific dispersant, further, among the physical properties of the carbon black dispersion composition, the viscosity minimum value and A shear rate of more than 1000 s ^-1 . The shear rate at which the viscosity has a minimum value indicates the state of dispersion of the carbon black in the composition. The carbon black dispersion composition having excellent battery characteristics according to the present invention can be obtained by setting the dispersion state such that the shear rate at which the viscosity has a minimum value is greater than 1000 s ^-1 .

The “shear rate at which the viscosity has a minimum value” in the present invention will be described in detail. The shear rate at which the viscosity has a minimum value refers to the shear rate at which the viscosity with respect to the shear rate has a minimum value. The shear rate at which the viscosity has a minimum value is a parameter that indicates the state of dispersion of carbon black in the composition and can be measured by a rheometer.
The shear rate at which the viscosity has a minimum value in the present invention is measured using MARSIII (manufactured by Thermo Fisher Scientific) as a measuring device, at a sensor DC of 60/2, at a constant temperature of 20 ° C., and at a shear rate of 0.01 to 3000 s ^−1. Can be obtained by reading the viscosity value with respect to the shear rate when the range is swept over 3 minutes as measurement data. When the viscosity value with respect to the shear rate in this measurement range changes from decrease to increase, it can be determined that the carbon black dispersion composition of the present invention has "shear rate at which the viscosity has a minimum value". Note that it is only necessary to confirm that the shear rate has a minimum value of the viscosity in the present measurement range, and the present invention is not limited to the above measurement conditions.

The relationship between shear rate and viscosity is determined by the interaction between particles in the fluid. Fluids are distinguished between Newtonian fluids and non-Newtonian fluids. The Newtonian fluid is a fluid having a viscous property in which the shear stress of the flow is proportional to the velocity gradient (shear rate) of the flow, and the non-Newtonian fluid is a fluid that does not exhibit the property. That is, the viscosity of a Newtonian fluid becomes constant even when the shear rate is changed, whereas the viscosity of a non-Newtonian fluid changes in accordance with the shear rate.
Non-Newtonian fluids are further classified into (1) structural viscosity and (2) danlatancy according to the flow behavior depending on the shear rate. (1) The structural viscosity decreases as the shear rate increases. This is because the particles form a more stable aggregated structure in the stationary state, but the aggregates are broken when a stress is applied to lower the viscosity. On the other hand, the viscosity of (2) dilatancy increases when the shear rate is high. The reason for this is that the one that is in the state of being filled in the stationary state does not have a filled structure when an external force is applied, and the particles are in direct contact with each other and behave like a solid.

The carbon black dispersion composition of the present invention exhibits (1) structural viscous behavior up to a certain shear rate, and (2) dilatancy behavior above a certain shear rate. Therefore, it exhibits a flow behavior having a minimum value of viscosity. The flow behavior changes at a certain shear rate (exceeding a certain shear rate causes dilatancy behavior). When the certain shear rate is reached, the movement of carbon black cannot keep up with that shear rate, This is because they are likely to flow in a state of a solid formed by contact with each other.
As the degree of dispersion of the dispersion composition increases, the cohesion between the carbon blacks is loosened, the interaction decreases, and the viscosity decreases, so that the carbon blacks easily move in the fluid, and the carbon blacks directly contact each other and behave like a solid. It becomes difficult. Therefore, the shear rate at which the flow behavior changes to the dilatancy behavior, that is, the shear rate having a minimum value of viscosity becomes larger. For such a reason, the shear rate at which the viscosity becomes a minimum value can be used as a parameter indicating the dispersion state of carbon black in the composition.

  The degree of dispersion of the carbon black dispersion composition in the mixture composition for a lithium ion secondary battery is important. The mixture composition for a lithium ion secondary battery can form an effective conductive path by using a carbon black dispersion composition in which carbon black is more dispersed, and expresses better conductivity. . If the dispersion is insufficient, the carbon black is unevenly distributed in the mixture layer, and the conductivity is reduced. They affect battery performance characteristics and cycle life.

Carbon black dispersion composition in the present invention, in the measurement of the rheometer ranges 0.01～3000S ^-1, shear rates as the viscosity minimum value when larger than 1000 s ^-1, to form an effective conductive path And found that the battery characteristics of the mixture composition were improved. Viscosity stability of the carbon black dispersion composition and a fixed combination composition using the same, in terms of the coating properties and coating uniformity of the mixture composition to better shear rate as the viscosity minimum value 1000 s ^- and more preferably in a larger 2000s ^-1 smaller range than ^1.

<Binder>
The carbon black dispersion composition of the present invention can further contain a binder. As the binder to be used, ethylene, propylene, vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acrylic acid, acrylic ester, methacrylic acid, methacrylic ester, acrylonitrile, styrene, vinyl butyral, vinyl acetal, vinyl pyrrolidone, etc. Polymer or copolymer containing as a structural unit; polyurethane resin, polyester resin, phenol resin, epoxy resin, phenoxy resin, urea resin, melamine resin, alkyd resin, acrylic resin, formaldehyde resin, silicone resin, fluororesin; styrene-butadiene Rubbers such as rubber and fluoro rubber; conductive resins such as polyaniline and polyacetylene; Further, modified products or mixtures of these resins, and copolymers may be used. Particularly, it is preferable to use a polymer compound having a fluorine atom in the molecule, for example, polyvinylidene fluoride, polyvinyl fluoride, tetrafluoroethylene or the like from the viewpoint of resistance.

  The weight average molecular weight of these resins as a binder is preferably 10,000 to 2,000,000, more preferably 100,000 to 1,000,000, and 200,000 to 1,000,000. Particularly preferred. If the molecular weight is small, the resistance and adhesion of the binder may be reduced. When the molecular weight is increased, the resistance and adhesion of the binder are improved, but the viscosity of the binder itself is increased and the workability is reduced, and at the same time, it acts as an aggregating agent, and the dispersed particles may aggregate significantly.

From the industrial applicability envisioned by the present invention, the binder preferably contains a polymer compound having a fluorine atom, is preferably a polymer compound having a fluorine atom, and is a vinylidene fluoride-based copolymer. More preferably, it is particularly preferably polyvinylidene fluoride.
In the industry, these binders are mainly used to obtain excellent resistance.However, due to the low adhesiveness of the resin, the adhesion to the base material when forming a coating film is weak and coating and processing are difficult. In many cases, it becomes difficult, and further, the viscosity may greatly increase in the presence of the basic metal oxide, which may cause a problem in storage stability. Therefore, there is a demand for a carbon black dispersion composition that maintains good adhesion and storage stability while using a vinylidene fluoride-based copolymer or polyvinylidene fluoride as a binder.

<Electrode active material>
The carbon black dispersion composition of the present invention can be used by further adding an electrode active material to the carbon black dispersion composition containing the above dispersant, carbon black as a carbon material, NMP as a solvent, and a binder.

As the positive electrode active material for the lithium ion secondary battery, although not particularly limited, metal oxides capable of doping or intercalating lithium ions, metal compounds such as metal sulfides, and conductive polymers are used. be able to.
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 , and TiO ₂ , lithium nickelate having a layered structure, lithium cobaltate, lithium manganate, and lithium manganate having a spinel structure can be used. Examples thereof include a composite oxide powder of lithium and a transition metal, a lithium iron phosphate-based material that is a phosphate compound having an olivine structure, and a transition metal sulfide powder such as TiS ₂ and FeS. Further, conductive polymers such as polyaniline, polyacetylene, polypyrrole, and polythiophene can also be used. Further, the above-mentioned inorganic compounds and organic compounds may be used as a mixture.

The negative electrode active material for a lithium ion secondary battery is not particularly limited as long as it can dope or intercalate lithium ions. For example, metal Li, alloys such as tin alloys, silicon alloys, alloys such as lead alloys, Li _x Fe ₂ O ₃ , Li _x Fe ₃ O ₄ , Li _x WO ₂ , lithium titanate, lithium vanadate, silicon Metal oxides such as lithium oxide, conductive polymers such as polyacetylene and poly-p-phenylene, amorphous carbonaceous materials such as soft carbon and hard carbon, artificial graphite such as highly graphitized carbon materials, or natural Examples of the material include carbonaceous materials such as carbonaceous powders such as graphite, carbon black, mesophase carbon black, resin-fired carbon materials, gas-grown carbon fibers, and carbon fibers. These negative electrode active materials can be used alone or in combination of two or more.

  The electrode active material used in the present invention preferably shows basicity in N-methyl-2-pyrrolidone, and more preferably the surface is not coated with a carbon material.

  The electrode active material used in the present invention preferably contains lithium and a metal element other than lithium as main constituent components, and more preferably a positive electrode active material.

  The positive electrode active material used in the present invention is preferably a composite oxide with lithium containing a transition metal such as Al, Fe, Co, Ni, and Mn, and lithium containing any of Al, Co, Ni, and Mn. And more preferably a composite oxide with lithium containing Ni and / or Mn. Particularly good effects can be obtained when these active materials are used.

These electrode active material preferably has a BET specific surface area of 0.1 to 10 m ² / g, more preferably a 0.2~5m ² / g, yet those 0.3~3m ² / g preferable.

  The average particle diameter of these electrode active materials is preferably in the range of 0.05 to 100 μm, and more preferably in the range of 0.1 to 50 μm. The average particle diameter of the electrode active material referred to in the present specification is an average value of the particle diameter measured by an electron microscope.

<Method for producing carbon black dispersion composition>
The carbon black dispersion composition of the present invention is obtained by dispersing carbon black in NMP using at least one polymer selected from methyl cellulose and ethyl cellulose as a dispersant. In this case, the dispersant and the carbon black are added simultaneously or sequentially and mixed, whereby the dispersant is dispersed while acting (adsorbing) on the carbon black. However, in order to more easily produce the carbon black dispersion composition, the dispersant is dissolved, swelled, or dispersed in NMP, and then the carbon black is added to the liquid and mixed to disperse the dispersant. It is more preferable to act (adsorb) on carbon black. Further, a dispersant and carbon black may be simultaneously charged into NMP to perform a dispersion treatment.

  As the dispersing device, a dispersing device usually used for pigment dispersion or the like can be used. For example, mixers such as disperser, homomixer, and planetary mixer, homogenizers (such as "Clearmix" manufactured by M Technique, Inc., "Fillmix" manufactured by PRIMIX, and "Abramix" manufactured by Silverson), paint conditioners ( Red Devil Co., Ltd., colloid mills ("PUC colloid mill" manufactured by PUC, "colloid mill MK" manufactured by IKA), cone mills ("corn mill MKO" manufactured by IKA, etc.), ball mills, sand mills (Shinmaru Enterprises Co., Ltd.) "Dino Mill", etc.), Attritor, Pearl Mill (e.g., "DCP Mill", etc.), Media Type Disperser such as Koball Mill, Wet Jet Mill ("Genus PY", manufactured by Genus, "Starburst", manufactured by Sugino Machine) , Nanomizer manufactured by Nanomizer ), M Technique Co., Ltd. "Claire SS-5", Nara Machinery Co., Ltd. "MICROS" media-less dispersing machine such as, but other roll mill, and the like, but is not limited to these.

  Next, a case in which a carbon black is subjected to a surface treatment with a dispersant by a dry treatment and then a dispersion composition is produced will be described. A carbon black dispersion composition can be obtained by adding and mixing a mixture of carbon black obtained by the following dry treatment and a dispersant into NMP. Examples of a method for obtaining carbon black surface-treated with a dispersant include a dry treatment method.

  In the dry treatment in the present invention, the dispersant acts (adsorbs) on the surface of the carbon black while mixing, pulverizing and the like of the carbon black and the dispersant by a dry treatment device at normal temperature or under heating. However, it is not necessary that the dispersant is completely adsorbed on the surface of the carbon black, and there is a case where there is no problem in practical use if the dispersant can be mixed homogeneously to some extent. The apparatus to be used is not particularly limited, and a media type dispersing machine such as a paint conditioner (manufactured by Red Devil), a ball mill, an attritor, a vibration mill, a kneader, a roller mill, a stone mill, a planetary mixer, a fen Medialess dispersing and kneading machines such as Shell Mixer, Hybridizer (Nara Machinery Co., Ltd.), Mechano Micros (Nara Machinery Co., Ltd.), and Mechano Fusion System AMS (Hosokawa Micron Co., Ltd.) can be used. It is more preferable to use a medialess dispersing / kneading machine in consideration of contamination and the like.

  At this time, an organic solvent may be added as long as the processed product does not become a gel. Improving the wetting or (partly) dissolution of the dispersant by the addition of the solvent and the wetting of the carbon black with the dispersant enhances the interaction between the carbon black and the dispersant. The solvent used at this time is not particularly limited, but when using other than NMP, it is desirable to dry after the treatment. The addition amount of the organic solvent varies depending on the material used, but is 0.5 to 100% by mass based on the addition amount of the dispersant. Furthermore, the processing may be performed by setting the inside of the dry processing apparatus to a deoxygenated atmosphere by flowing nitrogen gas or the like as necessary.

  The dry processing time can be arbitrarily set depending on the apparatus used and the desired degree of kneading. By performing these dry treatments, a powdery or lumpy processed material can be obtained. The obtained processed product may be further dried and pulverized thereafter.

  The carbon black dispersion composition of the present invention is a carbon black dispersion composition containing the above dispersant, carbon black as a carbon material, N-methyl-2-pyrrolidone as a solvent, and a binder and an electrode active material. It is preferably used as a dispersion composition (hereinafter, referred to as “mixture paste”).

  This mixture paste can be produced by mixing the dispersant, the carbon material, the solvent, the binder, and the electrode active material. There is no particular limitation on the order of addition of each component, for example, a method of mixing all components at once, a method of mixing by adding the remaining components to the carbon material dispersion composition prepared in advance by the above-described method, A method in which the electrode active material is added to the carbon material-dispersed varnish prepared in advance by the above-described method and mixed is used.

  As a device for producing the mixture paste, the same device as that used when producing the above-described dispersion composition of the present invention can be used.

<Battery>
Next, a battery using the composition of the present invention will be described. The composition of the present invention can be particularly suitably used for a lithium ion secondary battery. Hereinafter, a lithium ion secondary battery will be described, but a battery using the composition of the present invention is not limited to a lithium ion secondary battery.

  A lithium ion secondary battery includes a positive electrode having a positive electrode mixture layer on a current collector, a negative electrode having a negative electrode mixture layer on a current collector, and a nonaqueous electrolyte made of an electrolyte containing lithium. I do.

  For the electrode, the material and shape of the current collector used are not particularly limited, and as the material, metals and alloys such as aluminum, copper, nickel, titanium, and stainless steel are used. Copper is preferably used as the material. Further, as the shape, generally, a flat foil is used, but a roughened surface, a perforated foil, or a mesh can also be used. In addition, a conductive base layer may be provided on the current collector for the purpose of improving the contact resistance and adhesion between the current collector and the mixture layer.

  The mixture layer can be formed by directly applying the mixture paste on the current collector and drying. The thickness of the mixture layer is generally 1 μm or more and 1 mm or less, preferably 100 μm or more and 500 μm or less. The application method 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 spray coating method, a gravure coating method, a screen printing method, and an electrostatic coating method. After the application, a rolling process using a lithographic press or a calender roll may be performed.

As an electrolytic solution constituting the lithium ion secondary battery, a solution obtained by dissolving an electrolyte containing lithium in a non-aqueous solvent is used. As the electrolyte, 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, LiBPh ₄ (where Ph is a phenyl group), but is not limited thereto.

  The non-aqueous solvent is not particularly limited, but carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate, γ-butyrolactone, γ-valerolactone, γ-octanoic lactone Such as lactones, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolan, 4-methyl-1,3-dioxolan, 1,2-methoxyethane, 1,2-ethoxyethane, 1,2-dibutoxyethane, etc. Glymes, esters such as methyl formate, methyl acetate and methyl propionate, sulfoxides such as dimethyl sulfoxide and sulfolane, nitriles such as acetonitrile, and N-methyl-2-pyrrolidone. . These solvents may be used alone or in combination of two or more. In particular, a mixture of ethylene carbonate and other solvents having a high dielectric constant and a high dissolving power of the electrolyte is preferable, and further, as other solvents, propylene carbonate, butylene carbonate, dimethyl carbonate, and linear carbonates such as ethyl methyl carbonate and diethyl carbonate. Solvents are more preferred.

  Further, the electrolyte solution may be a gelled polymer electrolyte held in a polymer matrix. Examples of the polymer matrix include, but are not limited to, an acrylate resin having a polyalkylene oxide segment, a polyphosphazene resin having a polyalkylene oxide segment, and a polysiloxane having a polyalkylene oxide segment.

  The structure of the battery using the composition of the present invention is not particularly limited, but usually includes a positive electrode and a negative electrode, and a separator provided as necessary, and is paper-type, cylindrical, square, button-type, and laminated. It can be formed into various shapes such as a mold and a wound mold according to the purpose of use.

Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited to the following Examples as long as the gist of the present invention is not exceeded. In this example, “part” represents “part by mass”, and “%” represents “% by mass”.
The carbon black (sometimes abbreviated as "CB"), dispersant, electrode active material, and the like used in Examples and Comparative Examples are shown below.

<Carbon black>
LITX (registered trademark) 200 (manufactured by CABOT): furnace black, specific surface area 130 m ² / g, hereinafter abbreviated as LITX 200.
LITX (registered trademark) HP (manufactured by CABOT): furnace black, specific surface area 100 m ² / g, hereinafter abbreviated as LITXHP.
Denka Black HS-100 (manufactured by Denka Corporation): acetylene black, specific surface area 39 m ² / g, hereinafter abbreviated as HS-100.
-Denka black granules (manufactured by Denka): acetylene black, specific surface area 69 m ² / g, hereinafter abbreviated as granules.
Denka Black FX-35 (manufactured by Denka): acetylene black, specific surface area 133 m ² / g, hereinafter abbreviated as FX-35.

<Dispersant>
<Methylcellulose / ethylcellulose>
-Metrolose SM-15 (manufactured by Shin-Etsu Chemical Co., Ltd.): methylcellulose, degree of substitution: 1.8, viscosity of 2% aqueous solution at 20 ° C: about 15 mPa · s, weight average molecular weight: about 70,000, abbreviated as MC-1.
Metrolose SM-4 (manufactured by Shin-Etsu Chemical Co., Ltd.): methylcellulose, degree of substitution 1.8, viscosity of 2% aqueous solution at 20 ° C. about 4 mPa · s, weight average molecular weight about 25,000, hereinafter abbreviated as MC-2.
Metrolose SM-25 (manufactured by Shin-Etsu Chemical Co., Ltd.): methylcellulose, degree of substitution 1.8, viscosity of a 2% aqueous solution at 20 ° C. about 25 mPa · s, weight-average molecular weight about 90,000, abbreviated as MC-3.
-Ethocel STD-4 (manufactured by Dow Chemical Company): Ethyl cellulose, viscosity of 5% toluene / ethanol (8/2) solution at 25 ° C 3.0 to 5.5 mPa · s, weight average molecular weight of about 40,000, EC Abbreviated as -1.
-Ethocel STD-10 (manufactured by Dow Chemical Company): ethyl cellulose, viscosity of 5% toluene / ethanol (8/2) solution at 25 ° C 9.0 to 11.0 mPa · s, weight average molecular weight about 80,000, EC Abbreviated as -2.

<Others>
-Kuraray Povar PVA-405 (manufactured by Kuraray Co., Ltd.): polyvinyl alcohol, saponification degree 82 mol%, average polymerization degree 500, hereinafter abbreviated as PVA-1.
-PVP K30 (manufactured by Nippon Shokubai Co., Ltd.): polyvinylpyrrolidone, molecular weight of about 40,000, hereinafter abbreviated as PVP-1.

<Binder>
-KF polymer W7300 (Kureha): polyvinylidene fluoride (PVDF), weight average molecular weight about 1,000,000. Hereinafter, it is abbreviated as PVDF.

<Electrode active material>
LiNi _1/3 Mn _1/3 Co _1/3 O ₂ (manufactured by Toda Kogyo): positive electrode active material, lithium nickel manganese cobaltate, average primary particle diameter 5.5 μm obtained by observation with an electron microscope, nitrogen The specific surface area determined by the S-BET equation from the amount of adsorption is 0.62 m ² / g, hereinafter abbreviated as NCM.
LiNi _0.8 Co _0.15 Al _0.05 O ₂ (manufactured by Sumitomo Metal Co., Ltd.): positive electrode active material, lithium nickel cobalt aluminate, average primary particle diameter determined by observation with an electron microscope, 5.8 μm, S-BET based on nitrogen adsorption The specific surface area obtained by the formula is 0.38 m ² / g, and is abbreviated as NCA hereinafter.

<Evaluation of carbon black dispersion composition>
The carbon black dispersion compositions obtained in Examples 1 to 14 and Comparative Examples 1 to 9 were evaluated by measuring (1) the shear rate at which the viscosity was minimized, and (2) the initial viscosity value and the rate of change in viscosity. Was. The evaluation method is as follows.

<Shear rate at which viscosity becomes minimum>
A rheometer: MARSIII (manufactured by Thermo Fisher Scientific), a sensor: DC60 / 2, constant at 20 ° C., and a flow curve was measured using a measurement range of 0.01 to 3000 s ⁻¹ . The carbon black dispersion composition of the present invention has a carbon black content, and the amount of the dispersant when at least one selected from methyl cellulose and ethyl cellulose is used as the dispersant is within the above-described range, and the viscosity has a minimum value. The production method is not limited as long as the shear rate becomes more than 1000 s ^-1 .

<Initial viscosity value and viscosity change rate>
The dispersion stability, which is a problem in the present invention, can be evaluated from the viscosity change rate of the obtained carbon black dispersion composition over time. The rate of change in viscosity was evaluated based on the rate of change in the measured viscosity after standing at 50 ° C. for 10 days based on the measured viscosity (initial viscosity) after dispersion. The smaller the change, the better the stability. The viscosity value was measured using a B-type viscometer (“BL” manufactured by Toki Sangyo Co., Ltd.) at a dispersion composition temperature of 25 ° C. and a B-type viscometer rotor rotation speed of 60 rpm. Immediately after stirring. The rotor used for the measurement was No. 1 when the viscosity value was less than 100 mPa · s. No. 1 is not less than 100 mPa · s and less than 500 mPa · s. 2 is 500 mPa · s or more and less than 2000 mPa · s. No. 3 is 2000 mPa · s or more and less than 10000 mPa · s. Four samples were used. The viscosity change rate was evaluated on the following four levels.
；: Absolute value of viscosity change rate within 20% (good)
△: Absolute value of viscosity change rate is within 50% (somewhat poor)
×: Absolute value of viscosity change rate exceeds 50% or gelation (poor)
-: Viscosity is already poor at the beginning (initial failure)

<Preparation of carbon black dispersion composition>
[Example 1]
A glass bottle was charged with 75 parts of N-methyl-2-pyrrolidone and 1 part of a dispersing agent MC-1. After thoroughly mixing and dissolving or mixing and dispersing, 24 parts of carbon black granules were added, and a paint conditioner was prepared using zirconia beads as a medium. Was dispersed. A 1300S ^-1 was measured shear rate as the viscosity minimum value, and terminates the dispersion for making sure that exceeds 1000 s ^-1, to obtain a carbon black dispersion composition D-1.

[Examples 2 to 16]
According to the composition shown in Table 1, a carbon black dispersion composition was prepared in the same manner as in Example 1. In all cases, the shear rate at which the viscosity had a minimum value was measured, and it was confirmed that the shear rate exceeded 1000 s ^{-1. The} dispersion was terminated, and carbon black dispersion compositions D-2 to 16 were obtained.

[Comparative Example 1]
A carbon black dispersion composition was prepared in the same composition and in the same manner as in Example 1. The obtained dispersion composition D-17 was completely dispersed at a shear rate of 750 s ^-1 at which the viscosity reached a minimum value.

[Comparative Examples 2 and 3]
A carbon black dispersion composition was produced in the same manner as in Example 1, except that the composition was changed to 20 parts of carbon black granules, 0.8 parts of dispersant MC-1 and 79.2 parts of N-methyl-2-pyrrolidone. . The dispersion composition was prepared at two points with a difference in shear rate at which the viscosity became a minimum value, the dispersion of carbon black dispersion D-18 was terminated at 500 s ⁻¹ , and the dispersion of carbon black D-19 was 1300 s ⁻¹ . Dispersion ended.

[Comparative Examples 4 and 5]
A carbon black dispersion composition was prepared in the same manner as in Example 1 except that the composition was changed to 15 parts of carbon black granules, 0.6 parts of dispersant MC-1 and 84.4 parts of N-methyl-2-pyrrolidone. . The dispersion composition was prepared at two points with a difference in shear rate at which the viscosity became a minimum value, the dispersion of carbon black dispersion composition D-20 was completed at 500 s ^-1 , and the composition of carbon black dispersion composition D-21 was at 1300 s ^-1 . Dispersion ended.

[Comparative Examples 6 to 9]
According to the composition shown in Table 1, a carbon black dispersion composition was prepared in the same manner as in Example 1. The carbon black dispersion composition D-22 (Comparative Example 6) had a high viscosity by being dispersed, and was difficult to take out. With respect to the other dispersion compositions, the shear rate at which the viscosity had a minimum value was measured, and it was confirmed that the shear rate exceeded 1000 s ^{-1. The} dispersion was terminated, and carbon black dispersion compositions D-23 to D-25 were obtained.

All of the carbon black dispersion compositions D-1 to D-16 obtained in Examples 1 to 16 had good viscosity stability even when dispersed until the shear rate at which the viscosity reached a minimum value was greater than 1000 s ^-1 .
According to the comparison between Example 1 and Comparative Example 1, when the shear rate at which the viscosity becomes a minimum value is 1000 s ^-1 or less, the dispersion stability of the conductive additive is somewhat poor, possibly due to dispersion in the dispersion degree of the conductive additive, and the carbon black dispersion composition Also in the evaluation of the substance itself, it was confirmed that it is effective to make the shear rate at which the viscosity becomes a minimum value larger than 1000 s ^-1 .
According to the comparison between Example 8 and Comparative Examples 2 to 5, when the content of carbon black is small, the dispersion stability is lowered irrespective of the progress of dispersion (shear rate at which the viscosity becomes a minimum value).
By comparing Example 1 with Comparative Examples 6 and 7, it was confirmed that the addition of the prescribed amount of the dispersant could balance the dispersibility and stability. In particular, if the amount of the dispersant is too small, the dispersibility becomes poor.
By comparison between Examples 1 to 5 and Comparative Examples 8 and 9, it was not possible to achieve both dispersibility and stability with a dispersant such as PVA or PVP at the specified amount, and MC or EC was used as a dispersant. Confirmed that it is valid.

<Preparation of carbon black dispersion composition containing positive electrode active material>
[Examples 17 to 35, Comparative Examples 10 to 18]
According to the composition shown in Table 2, the binder and the positive electrode active material were charged into the carbon black dispersion compositions (D-1 to 25) obtained in Examples 1 to 16 and Comparative Examples 1 to 9 and thoroughly mixed by a disper. And carbon black dispersion compositions (carbon black mixture paste) BC-1 to 28 containing a positive electrode active material.

<Evaluation of carbon black dispersion composition containing positive electrode active material>
The carbon black mixture pastes obtained in Examples 17 to 35 and Comparative Examples 10 to 18 were evaluated by (1) coating color measurement and (2) resistance measurement of a battery electrode film. The battery characteristics of the carbon black dispersion composition can be evaluated by measuring the uniformity of the coating by measuring the color of the coating of the carbon black mixture paste and measuring the resistance of the obtained battery electrode film. The evaluation method is as follows.

<Coating color measurement>
Each of the carbon black mixture pastes BC-1 to 28 obtained in each of the above Examples and Comparative Examples was coated on a PET film using a doctor blade, and then dried at 140 ° C. for 5 minutes. A coating film of 100 μm was produced. The evaluation of the obtained coating film was performed by measuring the lightness (L value) of the front surface and the back surface of the coating film using a spectral color difference meter (SE-6000, manufactured by Nippon Denshoku Industries Co., Ltd.), and determining the lightness difference ΔL. evaluated. A smaller ΔL indicates a more uniform coating film. The measurement was performed using a C / 2 light source, and the wavelength range was 380 to 780 nm.
The lightness difference was evaluated on the following three levels.
（(Good): ΔL ≦ 5
Δ (slightly poor): 5 <ΔL ≦ 10
× (bad): ΔL> 10
If the dispersion state of the carbon black dispersion composition is insufficient, the electrode active material and carbon are biased in the mixture layer. In the more uniformly dispersed dispersion composition, when mixed with the electrode active material, they are mixed uniformly, and even when a coating film is formed, carbon black as a conductive additive can be present in the electrode active material without bias. A small difference in brightness between the front and back of the coating indicates that the coating is more uniform.

<Measurement of resistance value of battery electrode film>
After applying the carbon black mixture paste BC-1 to 28 obtained in each of the above Examples and Comparative Examples on a PET film using a doctor blade, the paste was dried under reduced pressure at 120 ° C. for 30 minutes, and then dried. A coating film (battery electrode mixture layer) having a thickness of 100 μm was prepared. As an evaluation of the obtained battery electrode film, a resistivity meter “Loresta GP” (Loresta GP MCP-T610 type resistivity meter, JIS-K7194 compliant, 4-terminal 4-probe method, constant current application method, manufactured by Mitsubishi Chemical Analytech) The volume resistivity (Ω · cm) of the battery electrode film was measured using a (4-terminal probe at 0.5 cm intervals).
The volume resistivity was evaluated on the following four scales.
◎ (excellent): less than 30 Ω · cm ○ (good): 30 Ω · cm or more and less than 50 Ω · cm △ (slightly poor): 50 Ω · cm or more and less than 70 Ω · cm × (bad): 70 Ω · cm or more

  The carbon black mixture pastes BC-1 to 19 obtained in Examples 17 to 35 are more uniform in coating film than the carbon black mixture pastes BC-20 to 28 obtained in Comparative Examples 10 to 18. It was clear that the battery electrode film had excellent resistance.

<Assembly of cell for evaluating positive electrode of lithium ion secondary battery>
[Examples 36 to 54, Comparative Examples 19 to 27]
A doctor blade was applied to the previously prepared carbon black mixture paste BC-1 to 28 (the mixture pastes of Examples 17 to 35 and Comparative Examples 10 to 18) on a 20 μm-thick aluminum foil serving as a current collector. After being applied and dried by heating at 120 ° C. under reduced pressure, it was rolled by a roller press to produce a positive electrode mixture layer having a thickness of 100 μm. This was punched out to a diameter of 9 mm as a working electrode, a metal lithium foil (thickness 0.15 mm) as a counter electrode, and a separator made of a porous polypropylene film (thickness 20 μm, porosity 50%) between the working electrode and the counter electrode. Insert and stack, fill with an electrolyte (a non-aqueous electrolyte in which LiPF ₆ is dissolved at a concentration of 1M in a mixed solvent of ethylene carbonate and diethyl carbonate at a volume ratio of 1: 1) and fill it with a bipolar closed metal cell (Treasure). Izumisha HS flat cell) was assembled. The cell was assembled in a glove box in which argon gas had been replaced.

<Evaluation of positive electrode characteristics of lithium ion secondary battery>
The prepared positive electrode evaluation cell was fully charged at 30 ° C. using a charge / discharge device (SM-8 manufactured by Hokuto Denko Corporation) at a constant current and constant voltage charge (upper limit voltage: 4.2 V) at a charge rate of 1.0 C. A charge / discharge cycle of discharging at a constant current of the same rate as that for charging to a discharge lower limit voltage of 3.0 V was defined as one cycle (charge / discharge interval pause time: 30 minutes), and this cycle was performed for a total of 50 cycles to perform charging / discharging. . The cell after the evaluation was disassembled in a glove box purged with argon gas, and the appearance of the electrode coating film (the coating film after 50 cycles) was visually checked. Table 3 shows the evaluation results.
The evaluation criteria for the appearance of the coating film are as follows.
（(Extremely good); no peeling from the current collector and no change in appearance 外 観 (good); no peeling but change in appearance × (poor); When the peeling is observed from the current collector, the capacity retention ratio is a percentage of the discharge capacity at the 50th cycle with respect to the discharge capacity at the first cycle, and the closer the value is to 100%, the better.
◎ (extremely good); when the capacity retention rate is 95% or more〇 (good); when the capacity maintenance rate is 90% or more and less than 95% △ (acceptable); when the capacity maintenance rate is 80% or more and less than 90% None (-); when a normal charge / discharge curve was not obtained due to peeling of the coating film from the current collector or a short circuit, and the capacity was not determined.

As shown in Table 3, Examples 36 to 54 using the electrode of the present invention also showed good results with respect to the coating film appearance and the capacity retention after 50 cycles as compared with Comparative Examples 19 to 27. .
On the other hand, in Comparative Examples 23 and 24, since a favorable coating film could not be obtained, the positive electrode characteristics could not be evaluated. In Comparative Examples 20, 22, 25 to 27, coating films could be obtained, but the positive electrode characteristics could not be evaluated because the dispersant dissolved or largely swelled in the electrolyte during the cycle test.

Claims (7)

A carbon black dispersion composition containing carbon black, a dispersant, and N-methyl-2-pyrrolidone, wherein the content of carbon black is 20.5 to 30% by mass, and the content of the dispersant is carbon black. 0.4 to 20 parts by mass with respect to 100 parts by mass, the dispersant is at least one selected from the group consisting of methylcellulose and ethylcellulose, and the shear rate at which the viscosity has a minimum value is 1000 s ^{−. A} carbon black dispersion composition characterized by being larger than ¹ . And wherein the shear rate as the viscosity minimum value is smaller than the larger 2000s ^-1 than 1000 s ^-1, of carbon black dispersion composition according to claim 1.   The carbon black dispersion composition according to claim 1 or 2, wherein the content of the dispersant is 1 part by mass or more and 10 parts by mass or less based on 100 parts by mass of carbon black.   The carbon black dispersion composition according to claim 1, further comprising a binder.   The carbon black dispersion composition according to any one of claims 1 to 4, further comprising an active material.   An electrode having a mixture layer formed of the carbon black dispersion composition according to claim 1 on a current collector.   A battery comprising the electrode according to claim 6 and a non-aqueous electrolyte.