JP2020021629A - Carbon black dispersion composition for battery and use thereof - Google Patents

Abstract

To provide: a carbon black dispersion composition for batteries, excellent in dispersibility, dispersion stability and coating film uniformity as compared with a carbon black dispersion liquid obtained by using well-known polymer type dispersant and dispersant amount, the carbon black dispersion composition having a high electrode active material content: and a battery electrode mixture layer.SOLUTION: A carbon black dispersion composition for batteries contains carbon black, a dispersant, and N-methyl-2-pyrrolidone, and further contains a binder and a positive electrode active material. The binder contains a polymer compound having at least a fluorine atom. The amount of the positive electrode active material with respect to 100 pts.mass of solid content of the dispersion composition is 97.8 pts.mass or more. The dispersant is at least one selected from the group consisting of methyl cellulose and ethyl cellulose. Further, the amount of the dispersant with respect to 100 pts.mass of the positive electrode active material is 0.05 pt.mass or more and 0.08 pt.mass or less.SELECTED DRAWING: None

Description

  The present invention relates to a carbon black dispersion composition for batteries having excellent dispersibility and coating properties. The invention also relates to a battery electrode mixture layer and a lithium ion secondary battery using the 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 order to reduce the amount of solvent used and the energy used for drying by creating a carbon material dispersion liquid with a higher concentration and uniform dispersion than before, especially considering the environment and production costs. 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. It is known that the stability and coating properties of a dispersion composition largely depend on the dispersant to be used. Have difficulty.

  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 layer formed using the dispersion composition disclosed in Patent Documents 1 and 2, the battery performance and the uniformity of the coating film are insufficient, and the amount of the active material in the electrode mixture layer is low. In a high-capacity battery with many components, the conductive assistant is not evenly distributed in the battery electrode mixture layer, and desired 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 dispersion composition containing carbon black, a dispersant, a binder, and an electrode active material. . However, the addition of an acidic compound to a dispersion composition having a large amount of active material is not desirable in that it may affect the stability and uniformity of the mixture, so that a formulation design without additives is required.

  Further, Patent Document 4 describes a nonaqueous electrolyte secondary battery including a positive electrode plate in which a positive electrode mixture layer containing 97.6% by mass or more of a positive electrode active material in a positive electrode mixture layer is formed, It also describes that a dispersant is contained in the positive electrode mixture layer. However, the carbon black dispersion composition is not described in detail including the composition, dispersibility and stability of the carbon black dispersion composition, there is no description about the issues and evaluation results such as uniformity, especially Since the amount of the dispersant, which is important for satisfying the battery characteristics, is not appropriate, there is a problem that the performance of the disclosed nonaqueous electrolyte secondary battery is insufficient.

WO 2014/042266 Patent No. 5628503 JP-A-2006-046188 Japanese Patent No. 6282595

  In view of the above circumstances, in the present invention, compared to the conventionally known polymer type dispersant and carbon black dispersion obtained using the dispersant amount, dispersibility, dispersion stability, and excellent coating film uniformity Further, to provide a battery carbon black dispersion composition and a battery electrode mixture layer having a high electrode active material content, further, using the battery carbon black composition and the battery electrode mixture layer, the electrode adhesion It is an object to provide a lithium ion secondary battery having excellent battery characteristics (cycle characteristics).

  The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, a dispersion composition using methylcellulose or ethylcellulose as a dispersant and further using a smaller amount than the conventional dispersant has a dispersibility and stability of the mixture. Has been found to be very effective in improving the uniformity of the coating film, and the present invention has been accomplished.

  That is, an embodiment of the present invention is a carbon black dispersion composition for a battery including carbon black, a dispersant, and N-methyl-2-pyrrolidone, and further including a binder and a positive electrode active material, The binder contains a polymer compound having at least a fluorine atom, and the amount of the positive electrode active material is 97.8 parts by mass or more with respect to 100 parts by mass of the solid content of the dispersion composition, and the dispersant comprises methyl cellulose and ethyl cellulose. At least one member selected from the group; and further, the amount of the dispersant is from 0.05 parts by mass to 0.08 parts by mass with respect to 100 parts by mass of the positive electrode active material. The present invention relates to a carbon black dispersion composition.

  Further, an embodiment of the present invention relates to the carbon black dispersion composition for a battery, wherein the dispersant is methylcellulose, and the weight average molecular weight of the dispersant is in the range of 20,000 to 200,000.

Further, an embodiment of the present invention relates to a method for producing the carbon black dispersion composition for a battery obtained by the following two steps.
A first step; a step of preparing a carbon black dispersion slurry by mixing and dispersing carbon black, a dispersant, and N-methyl-2-pyrrolidone; a second step; a carbon black dispersion slurry obtained in the previous step And mixing and dispersing the positive electrode active material and the binder

  Further, an embodiment of the present invention relates to a battery electrode mixture layer formed by applying the carbon black dispersion composition for a battery.

  Further, an embodiment of the present invention provides a lithium ion secondary battery including 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 an electrolyte containing lithium. And a lithium ion secondary battery in which a positive electrode includes the battery electrode mixture layer.

  Hereinafter, details of the present invention will be described. In the present specification, "carbon black dispersion composition", "carbon black dispersion composition for batteries" is "dispersion composition", "N-methyl-2-pyrrolidone" is "NMP", "positive electrode active material or “Negative electrode active material” may be abbreviated as “electrode active material” or “active material”.

<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 is preferably 0.01 to 1 μm, as in the case of the average primary particle size of the carbon black used in general dispersion compositions and coatings. It is preferably from 0.01 to 0.2 μm, more preferably from 0.01 to 0.1 μm. 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.

  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 a too 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 dispersion 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.

<Binder>
The carbon black dispersion composition for batteries of the present invention further contains a binder. From the industrial applicability assumed by the present invention, the binder includes a polymer compound having a fluorine atom. The polymer compound having a fluorine atom is preferably a vinylidene fluoride-based copolymer, and more 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.

  Further, as the binder to be used, the following resins may be used in combination. As the combined resin, ethylene, propylene, vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acrylic acid, acrylic acid ester, methacrylic acid, methacrylic acid ester, acrylonitrile, styrene, vinyl butyral, vinyl acetal, vinyl pyrrolidone, etc. Polymer or copolymer containing as a unit; polyurethane resin, polyester resin, phenol resin, epoxy resin, phenoxy resin, urea resin, melamine resin, alkyd resin, acrylic resin, formaldehyde resin, silicone resin, fluororesin; like carboxymethylcellulose Cellulosic resins; rubbers such as styrene-butadiene rubber and fluororubber; modified products and mixtures of conductive resins such as polyaniline and polyacetylene; and copolymers.

  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.

<N-methyl-2-pyrrolidone>
The carbon black dispersion composition for a battery 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.

<Active material>
An active material is a substance that sends or receives electrons and performs an oxidation or reduction reaction in a battery. A positive electrode active material used for the positive electrode and a negative electrode active material used for the negative electrode are given.

<Positive electrode active material>
The carbon black dispersion composition for a battery of the present invention further contains a positive electrode active material.

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

  In order to obtain a higher capacity nonaqueous electrolyte secondary battery, the amount of the positive electrode active material in the present invention is 97.8 parts by mass or more based on 100 parts by mass of the solid content of the carbon black dispersion composition for a battery. .

<Negative electrode active material>
The negative electrode active material to be used is not particularly limited, but a metal Li capable of doping or intercalating lithium ions, or an alloy thereof, a tin alloy, a silicon alloy negative electrode, Li _X Fe ₂ O ₃ , Li _X Fe ₃ O ₄ , Li _X WO ₂ or the like of the metal oxide-based, polyacetylene conductive polymers poly -p- phenylene, or amorphous-based carbon material such as soft carbon or hard carbon, artificial graphite such as highly graphitized carbon material or, Carbonaceous materials such as carbonaceous powder such as natural graphite, carbon black, mesophase carbon black, resin fired carbon material, gas-grown carbon fiber, and carbon fiber are used. Here, x is a number, and 0 <x <1. These negative electrode active materials can be used alone or in combination of two or more.

These 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, further preferably from 0.3~3m ² / g .

  These active materials preferably have an average particle diameter 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 active material referred to in the present specification is an average value of the particle diameter of the active material 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, a positive electrode active material, and a binder in NMP using one or more polymers selected from methyl cellulose and ethyl cellulose as a dispersant. With the composition of the present invention, a carbon black dispersion composition having a target quality or higher can be obtained regardless of the production method described below.

  The dispersant and carbon black are added simultaneously or sequentially and mixed, so that 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 preferable to cause the carbon black to act (adsorb).

  A dispersant, carbon black, a positive electrode active material, and a binder may be simultaneously charged and dispersed in NMP. However, from the viewpoint of further improving the dispersibility of the carbon black dispersion composition and the battery characteristics using the same, it is more preferable that the composition can be obtained through the following two steps. The first step of the two steps is a step of mixing and dispersing carbon black, a dispersant and NMP (the resulting dispersion is referred to as “carbon black dispersion slurry”), and the second step is And mixing and dispersing the carbon black dispersion slurry obtained in the previous step, the positive electrode active material, and the binder.

  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 carbon black is subjected to a surface treatment with a dispersant by a dry treatment and then a dispersion 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.

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

  In the present invention, the addition amount of methylcellulose and ethylcellulose as a dispersant for carbon black is preferably 1 part by mass or more and 15 parts by mass or less, more preferably 4 parts by mass or more and 10 parts by mass or less based on 100 parts by mass of carbon black. More preferably, it is 4 parts by mass or more and 8 parts by mass or less.

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

In the present invention, the addition amount of methylcellulose and ethylcellulose as the dispersant is 0.05 parts by mass or more and 0.08 parts by mass with respect to 100 parts by mass of the positive electrode active material contained in the carbon black dispersion composition for a battery. Or less, and preferably 0.05 to 0.07 parts by mass.
For the positive electrode active material, if the amount of the dispersant is too large, not only will the relative solid content ratio occupied by the active material and the conductive agent decrease, but the dispersant elutes or swells in the electrolytic solution, The chemical stability and physical shape stability of the battery electrode mixture layer may be deteriorated.

  In the present invention, the addition amount of the binder is preferably 0.5 parts by mass or more and less than 20 parts by mass, and more preferably 0.5 parts by mass or more, based on 100 parts by mass of the positive electrode active material contained in the carbon black dispersion composition for a battery. 10 parts by mass or less, more preferably 0.5 parts by mass or more and 5 parts by mass or less, particularly preferably 0.5 parts by mass or more and 2 parts by mass or less.

  By blending at the above ratio, the dispersibility and coating suitability of the carbon black dispersion composition for a battery, which is a problem to be solved by the present invention, can be improved, and dispersibility, coating suitability, and battery characteristics can be improved. It becomes easy to obtain an excellent dispersion.

<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 an electrolyte containing lithium.

  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 electrode mixture layer can be formed by directly applying the above-mentioned electrode mixture paste on the current collector and drying the paste. The thickness of the electrode mixture layer is generally from 1 μm to 500 μm, preferably from 10 μm to 300 μm. 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, Examples include, but are not limited to, LiI, LiBr, LiCl, LiAlCl, LiHF ₂ , LiSCN, LiBPh ₄ (where Ph is a phenyl group).

  The non-aqueous solvent is not particularly limited, but carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, γ-butyrolactone, γ-valerolactone, γ-octanoic lactone And the like, 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 1-methyl-2-pyrrolidone. . These solvents may be used alone or in combination of two or more.

  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.

  Examples of the separator include a polyethylene nonwoven fabric, a polypropylene nonwoven fabric, a polyamide nonwoven fabric and those obtained by subjecting them to a hydrophilic treatment, but are not particularly limited thereto.

  Although the structure of the battery using the composition of the present invention is not particularly limited, it is usually composed of a positive electrode and a negative electrode, and a separator provided as necessary, a paper type, a cylindrical type, a button type, a laminated type, and the like. Various shapes can be formed according to the purpose of use.

In the present invention, conventionally known dispersants, resins, additives, and the like may be used in combination for the purpose of adjusting the properties of the coating film and the like within a range that does not interfere with the above-described problems.
Examples of such dispersants include conventionally known dye derivatives, resin-type dispersants, and low molecular weight surfactants. As the resin, for example, polyvinylidene fluoride, polytetrafluoroethylene, polyhexafluoropropylene, polyethylene, polypropylene, polymethyl methacrylate, polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, polyacrylic acid, polyacrylamide, polyurethane , Polydimethylsiloxane, epoxy resin, acrylic resin, polyester resin, melamine resin, phenolic resin, various rubbers such as styrene butadiene rubber, lignin, pectin, gelatin, xanthan gum, welan gum, succinoglycan, cellulose resin, polyalkylene oxide, Examples include polyvinyl ether, chitins, chitosans, and starch. Examples of the additives include phosphorus compounds, sulfur compounds, amine compounds and amide compounds, organic esters, various silane-based, titanium-based, and aluminum-based coupling agents. These conventionally known dispersants, resins, additives and the like can be used alone or in combination of two or more.

<Use of carbon black dispersion composition for batteries>
The field of use of the carbon black dispersion composition for batteries of the present invention is suitably used for electrodes for lithium ion secondary batteries, electrodes for electric double layer capacitors, electrodes for lithium ion capacitors, and the like.

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, binder, 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 a 2% aqueous solution at 20 ° C: about 15 mPa · s, weight average molecular weight: 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 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 90,000, hereinafter 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 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 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 (manufactured by Kureha Corporation): polyvinylidene fluoride, weight average molecular weight about 1,000,000. Hereinafter, it is abbreviated as PVDF.
-KF polymer W1100 (manufactured by Kureha Corporation): polyvinylidene fluoride, weight average molecular weight about 280000. Hereinafter, it is abbreviated as # 1100.

<Electrode active material>
LiNi _1/3 Mn _1/3 Co _1/3 O ₂ (manufactured by Toda Kogyo KK): positive electrode active material, lithium nickel manganese cobaltate, average primary particle diameter determined by observation with an electron microscope of 5.0 μm, 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.

<Preparation of carbon black dispersion composition for battery>
[Example 1]
In a glass bottle, 25 parts of NMP and 0.05 parts of MC-1 were charged and mixed and dissolved sufficiently. Next, 1.0 part of carbon black granules was charged and dispersed with a homogenizer for 30 minutes to prepare a carbon black dispersion slurry. Thereafter, 1.0 part of PVDF and 98 parts of NCM were charged, and sufficiently mixed and dispersed by a disper to obtain a carbon black dispersion composition BC-1 for a battery.

[Example 2]
Unlike Example 1, the carbon black dispersion composition for a battery was prepared by a method of charging and dispersing all of the electrode active material and the binder at once without going through the preparation of a carbon black dispersion slurry composed of carbon black, a dispersant, and a solvent. Was prepared.
In a glass bottle, 25 parts of NMP and 0.05 parts of MC-1 were charged and mixed and dissolved sufficiently. Next, 1.0 part of carbon black granules, 1.0 part of PVDF, and 98 parts of NCM were all charged, and then sufficiently mixed and dispersed by a disper to obtain a carbon black dispersion composition BC-2 for a battery.

[Examples 3 to 9, 11 to 16, Comparative Examples 3, 5 to 7]
According to the composition shown in Table 1, in the same manner as in Example 1, carbon black dispersion compositions BC-3 to 9, 11 to 17, 19, and 21 to 23 for batteries were produced.

[Example 10, Comparative Examples 2 and 4]
According to the composition shown in Table 1, in the same manner as in Example 2, carbon black dispersion compositions BC-10, 18, and 20 for batteries were produced.

<Evaluation of carbon black dispersion composition for battery>
Evaluation of the carbon black dispersion compositions for batteries obtained in Examples and Comparative Examples was performed by (1) particle size measurement, (2) viscosity stability evaluation, and (3) filtration test. By the particle size measurement (1) and the evaluation of viscosity stability (2), the dispersibility and dispersion stability of the carbon black dispersion composition, which is the subject of the present invention, can be confirmed. Further, the dispersion stability of the carbon black dispersion composition can be confirmed by (3) a filtration test. The evaluation method is as follows.

<Particle size measurement>
The carbon black dispersion compositions produced in Examples and Comparative Examples were determined by a grind gauge (according to JIS K5600-2-5).
A: Coarse particles can be confirmed at a position of 15 μm or more and less than 20 μm by a grind gauge. (excellence)
：: Coarse particles can be confirmed by a grind gauge at a position of 20 μm or more and less than 50 μm. (Good)
×: Coarse particles can be confirmed at a position of 50 μm or more and less than 200 μm, or 200 μm or more by a grind gauge. (Bad)

<Viscosity stability evaluation>
The rate of change in viscosity was evaluated based on the rate of change in the measured viscosity after standing at 50 ° C. for 3 days, based on the measured 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.) and the dispersion composition was sufficiently stirred with a spatula at a dispersion temperature of 25 ° C. and a B-type viscometer rotor rotation speed of 60 rpm. And then went immediately. 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 three scales.
；: Absolute value of viscosity change rate is 20% or less (good)
△: Absolute value of viscosity change rate exceeds 20% and 50% or less (somewhat poor)
×: Absolute value of viscosity change rate exceeds 50% or gelation (poor)

<Filtration test>
The carbon black dispersion composition after standing and stored at 50 ° C. for 3 days is passed through a SUS mesh screen having an aperture of 100 μm, and the residue remaining on the screen without passing through the screen is collected and then dried at 140 ° C. for 1 hour. I let it. The solid content of the dried residue was measured, and the filterability was evaluated on the following three scales based on the ratio of the solid content of the residue to the total solid content of the carbon black dispersion composition passed through.
；: 0% or more and less than 10% (good)
Δ: 10% or more and less than 20% (somewhat poor)
×: 20% or more (defective)

All of the carbon black dispersion compositions BC-1 to 16 obtained in Examples 1 to 16 had good dispersion particle size and good filterability.
Comparison of Examples 1 to 2 and 5 with Comparative Examples 1 to 4 show that both the dispersibility and stability are improved by adding and dispersing a prescribed amount of a dispersant regardless of the method of preparing the dispersion composition. Was done. If the amount of the dispersant is too large, even if a certain degree of dispersibility is obtained, the stability becomes poor, and the uniformity of the coating film and the battery characteristics described later are adversely affected. If the amount of the dispersant is too small, dispersibility will be poor.
From Examples 1 and 6 to 9 and Comparative Examples 5 and 6, the use of methylcellulose or ethylcellulose as a dispersant allows the dispersibility and stability to be improved with a limited dispersant amount in a mixture composition having a high active material content. It shows that they can be compatible.

<Preparation of battery electrode mixture layer>
[Examples 17 to 32, Comparative Examples 8 to 14]
Each of the above Examples and Comparative Examples, the carbon black dispersion composition for a battery containing a positive electrode active material was applied as a battery electrode mixture liquid on an aluminum foil using a doctor blade, and then applied under reduced pressure to 120. It dried at 30 degreeC for 30 minutes, and produced the coating film (battery electrode mixture layer) L-1-23 of 100-micrometer-thickness after drying.
The evaluation of the obtained battery electrode mixture layer was performed by evaluating the appearance and uniformity of the coating film.
The appearance of the coating film was visually evaluated as ○: no problem (good), Δ: mottled pattern (good), ×: coarse grain streaks (extremely poor). The uniformity of the coating film was determined by measuring the lightness (L value) of the front and back surfaces of the coating film using a spectral colorimeter (SE-6000, manufactured by Nippon Denshoku Industries Co., Ltd.), and evaluating the lightness difference ΔL. A smaller ΔL indicates that the coating film is more uniform. The measurement was performed using a C / 2 light source, and the wavelength range was 380 to 780 nm. The lightness difference ΔL was evaluated on the following three levels. The results are shown in Table 2.
：: ΔL ≦ 5 (good)
Δ: 5 <ΔL ≦ 10 (somewhat defective)
×: 10 <ΔL (bad)

  From Table 2, the battery electrode mixture layers (L-1 to 16) of Examples 17 to 32 have a coating film appearance that is lower than that of the battery electrode mixture layers (L-17 to 23) of Comparative Examples 8 to 14. It became clear that the coating film uniformity was good. With L-17 to 23, the coating properties were poor due to the poor viscosity stability of the carbon black dispersion composition used, and good results could not be obtained in the appearance of the coating film. Further, the uniformity of the coating film could not be obtained due to poor dispersibility of the active material and carbon black in the dispersion composition.

<Assembly of cell for evaluating positive electrode of lithium ion secondary battery>
[Examples 33 to 48, Comparative Examples 15 to 21]
The previously prepared carbon black dispersion composition for a battery (BC-1 to BC-23) is applied on a 20 μm-thick aluminum foil serving as a current collector using a doctor blade, and then heated at 120 ° C. under reduced pressure. After drying, the resultant was subjected to a rolling treatment with a roller press to prepare 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. Regarding the adhesion of the electrodes, the evaluation criteria for the appearance of the coating film were as follows: ○ (excellent) when no peeling from the current collector was observed and no change in appearance, and when there was no peeling but no change in appearance △ (good) and × (poor) when the mixture layer was partially peeled off 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. ◎ (very good) when the capacity retention rate is 95% or more, （(good) when the capacity maintenance rate is 90% or more and less than 95%, and Δ (good) when the capacity maintenance rate is 80% or more and less than 90%. ), 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, the value was regarded as no value (-). Table 3 shows the evaluation results.

As shown in Table 3, Examples 33 to 48 using the electrode of the present invention showed good results in the appearance of the coating film and the capacity retention after 50 cycles as compared with Comparative Examples 15 to 21. On the other hand, in Comparative Examples 15 and 19 to 20, 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. In Comparative Examples 16 to 18 and 21, a good coating film could not be obtained, and thus the positive electrode characteristics could not be evaluated.

Claims (5)

  A carbon black dispersion composition for a battery, comprising: carbon black, a dispersant, and N-methyl-2-pyrrolidone, and further comprising a binder and a positive electrode active material, wherein the binder has at least a fluorine atom. Including a compound, the amount of the positive electrode active material with respect to 100 parts by mass of the solid content of the dispersion composition is 97.8 parts by mass or more, and the dispersant is at least one selected from the group consisting of methyl cellulose and ethyl cellulose. The carbon black dispersion composition for a battery, wherein the amount of the dispersant is 0.05 to 0.08 parts by mass based on 100 parts by mass of the positive electrode active material.   The carbon black dispersion composition for a battery according to claim 1, wherein the dispersant is methyl cellulose, and the weight average molecular weight of the dispersant is in the range of 20,000 to 200,000. The method for producing a carbon black dispersion composition for a battery according to claim 1 or 2, which is obtained by the following two steps.
A first step; a step of preparing a carbon black dispersion slurry by mixing and dispersing carbon black, a dispersant, and N-methyl-2-pyrrolidone; a second step; a carbon black dispersion slurry obtained in the previous step And mixing and dispersing the positive electrode active material and the binder   A battery electrode mixture layer formed by applying the carbon black dispersion composition for a battery according to claim 1 or 2.   A lithium ion secondary battery comprising a positive electrode having a positive electrode material mixture layer on a current collector, a negative electrode having a negative electrode material mixture layer on a current collector, and an electrolyte containing lithium, wherein the positive electrode is used. A lithium ion secondary battery comprising the battery electrode mixture layer according to any one of the preceding claims.