JP2016046188A - Carbon black dispersion and use of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a carbon black dispersion for a cell, which contains an active substance and is excellent in storage stability compared to a dispersion using a conventionally known polymeric dispersant, and to provide a cell electrode mixture solution that gives homogeneous and high coating film properties in a coating film thereof with excellent adhesiveness to a substrate even when a dispersion after long-term storage is used, and a cell electrode mixture layer.SOLUTION: A carbon black dispersion for a cell comprises carbon black, a binder, an acidic compound, a dispersant, an active substance, and N-methyl-2-pyrrolidone. The binder comprises a polymeric compound having a fluorine atom; the dispersant is at least one polymer selected from the group consisting of polyvinyl alcohol, polyvinyl acetal, polyvinyl butyral, and polyvinyl formal; and the total amount of the dispersant and the acidic compound is 0.05 parts by mass or more and 2.5 parts by mass or less with respect to 100 parts by mass of the active substance.SELECTED DRAWING: None

Description

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

  In the battery field, carbon black is widely used as a conductive additive, but when forming a battery electrode mixture layer, in order to shorten the production process in an efficient manner, the carbon black can be increased in a solvent. It is important to make it possible to easily disperse in concentration and uniformly.

In recent years, especially in consideration of the environment and production costs, the amount of solvent used and the energy used during drying have been reduced by producing a carbon black dispersion with a higher concentration and uniformity than before. It is requested to do.
Since these requirements have a great influence on the cost of the solvent and the energy used during drying, the more expensive the solvent used or the higher the boiling point of the solvent used, the more important. N-methyl-2-pyrrolidone used in non-aqueous secondary batteries is more expensive than common solvents and has a very high boiling point of 200 ° C. or higher. Since energy is required, reduction of the amount of solvent used in the dispersion is strongly demanded.

  In order to disperse a large amount of carbon black in a solvent, it is particularly effective to adsorb a dispersant on the surface of the carbon black so that the dispersion is in a stable state. Carbon using various dispersants Black dispersions have been proposed.

  In general, when carbon black is dispersed using a dispersant, the dispersibility of the carbon black is deteriorated when the amount of the dispersant is extremely reduced, and on the contrary, the dispersibility is improved when the amount of the dispersant is extremely increased. However, when used in battery applications, it is expected to adversely affect battery characteristics such as an increase in resistance and deterioration in conductivity.

  For example, Patent Documents 1 to 3 describe a coating liquid containing carbon black, unmodified or modified polyvinyl alcohol, a crosslinking agent (organic acid), and N-methyl-2-pyrrolidone. Document 1 describes that a positive electrode active material or a negative electrode active material is added to the coating solution to produce an electrode plate of a lithium ion secondary battery. However, since these polyvinyl alcohols in Patent Documents 1 to 3 are not sufficiently resistant to an electrolytic solution by themselves to be used as a binder (resin binder), an organic acid is used in combination as a crosslinking agent. Therefore, there is no technical idea of using polyvinyl alcohol as a dispersant.

On the other hand, in Patent Document 4, a carbon black dispersion containing N-methyl-2-pyrrolidone using polyvinyl alcohol having a saponification degree of 60 to 85 mol% as a dispersant is used. In Patent Document 5, polyvinyl acetal is used. Each carbon black dispersion used as a dispersant is described, and it is described that a carbon black dispersion having a high concentration is obtained while maintaining a good viscosity.
However, when a battery carbon black dispersion is prepared using such a polyvinyl alcohol or polyvinyl acetal as a dispersant, the viscosity may be difficult to apply, when a high molecular weight binder is used, and / Or use of electrode active materials with large specific surface area, strong basicity, Al, Ni, Mn, etc., the viscosity of the dispersion will increase significantly over time, making coating difficult That the coating film obtained using the dispersion liquid has insufficient adhesion to the substrate, and there may be concerns about the production process of the coating film and the homogeneity of the coating film, The inventor found out.
Carbon black dispersions are required to be easy to apply, have good storage stability, and better adherence of the coating to the substrate. There is a need for the development of black dispersions.

  In general, it is known that the viscous behavior of a dispersion is greatly influenced by the types and composition ratios of the components constituting the dispersion, and only a part of the structure of the material used as the dispersant is changed or is extremely different. It is expected that it is difficult to control the viscous behavior only by adding a small amount of additive. In addition, it is known that the storage stability of the dispersion largely depends on the dispersant used, but it is generally difficult to greatly improve the storage stability without changing the dispersant used.

In addition, it is known that the effect of the dispersant may vary greatly depending on the environment in which the dispersion is placed, such as pH, ionic strength, contained material, etc. The function and storage stability of the dispersant may be deteriorated just by adding.
By using a small amount of additives, the storage stability is greatly improved without adversely affecting the dispersion of carbon black. Furthermore, two or more types having different properties such as carbon black and electrode active materials. It is expected that it is difficult to select an additive that obtains only the expected effect in the dispersion containing the particles.

  Furthermore, when a dispersion whose viscosity has been greatly increased by storage is used as a coating film, the coating film may become inhomogeneous and adhesion may deteriorate. In order to compensate for this deterioration in adhesion, it is possible to further increase the binder, but this is not preferable because the ratio of other components is reduced. In addition, the polymeric dispersant itself may be a material having a function as a binder, but generally when used as a dispersant, only a trace amount is contained in the coating film, so it is simply It is expected that it is difficult to improve the adhesion by causing the polymer type dispersant to function as a binder, and it is desired to improve the storage stability which is the source of the problem.

  However, in order to obtain a carbon black dispersion that can improve the viscosity behavior, storage stability and adhesion to the substrate of the dispersion, the type of polymer dispersant used, its molecular structure, and each structural unit that constitutes the molecule In addition, no examples have been reported in detail about the ratio of the additive material used and the ratio and the ratio of the additive material used in combination, and the type and ratio of the material and additive used as the dispersant are viscous behavior and storage stability. The actual situation is that no consideration has been given to how it affects the adhesion.

International Publication No. 2009/147789 International Publication No. 2011/024799 JP 2013-48043 A Patent No. 5454725 JP 2011-184664 A

  In view of the above situation, in the present invention, compared to a carbon black dispersion obtained by using a conventionally known polymer-type dispersant alone, N-methyl-2-2, which is excellent in the storage stability of the dispersion. It is an object to provide a carbon black dispersion for batteries using pyrrolidone as a solvent. Also provided is a battery electrode mixture liquid and a battery electrode mixture layer that have excellent adhesion to the substrate when converted into a coating film even after using a dispersion after long-term storage, and that provide a uniform and good coating film property. It is a problem to do.

  The present inventors paid attention to the physical and chemical properties of carbon black, a dispersant, an additive, a binder, and an electrode active material, and as a result of detailed examination of their quantitative relationship, polyvinyl alcohol as a dispersant, By using one or more polymers selected from the group consisting of polyvinyl acetal, polyvinyl butyral, and polyvinyl formal as an additive, an acidic compound is used, so that storage stability is good even in the presence of an electrode active material, and coating properties are improved. The present inventors have found that it is possible to produce a carbon book dispersion which is excellent and has good adhesion to the substrate when it is formed into a coating film, and the present invention has been completed.

  That is, an embodiment of the present invention is a carbon black dispersion liquid containing carbon black, a binder, an acidic compound, a dispersant, a positive electrode active material or a negative electrode active material, and N-methyl-2-pyrrolidone. The binder contains at least a polymer compound having a fluorine atom, and the dispersant is one or more polymers selected from the group consisting of polyvinyl alcohol, polyvinyl acetal, polyvinyl butyral, and polyvinyl formal, The total amount of the dispersing agent and the acidic compound with respect to 100 parts by mass of the negative electrode active material is 0.05 parts by mass or more and 2.5 parts by mass or less.

  An embodiment of the present invention is characterized in that the polymer compound having a fluorine atom with respect to 100 parts by mass of the positive electrode active material or the negative electrode active material is contained in an amount of 0.5 parts by mass or more and less than 20 parts by mass. And the carbon black dispersion.

  In another embodiment of the present invention, the carbon black dispersion is characterized in that the dispersant is contained in an amount of 0.04 parts by mass or more and less than 2 parts by mass with respect to 100 parts by mass of the positive electrode active material or the negative electrode active material. Regarding liquids.

  In another embodiment of the present invention, the carbon black dispersion is characterized in that the acidic compound is contained in an amount of 0.01 parts by mass or more and less than 1 part by mass with respect to 100 parts by mass of the positive electrode active material or the negative electrode active material. Regarding liquids.

  Further, in an embodiment of the present invention, the acidic compound is an organic acid having one or more acidic functional groups selected from the group consisting of a carboxyl group, a sulfonic acid group, a phosphoric acid group, and a thiol group, or 1,3- The carbon black dispersion is a diketone.

  An embodiment of the present invention also relates to the carbon black dispersion, wherein the acidic compound has one or two acidic functional groups in the molecule and has a molecular weight of 1000 or less.

Further, in an embodiment of the present invention, the dispersant is a polyvinyl alcohol containing 50 to 95 mol% of a repeating unit represented by the following general formula (A) in a polymer chain, and dispersed with respect to 100 parts by mass of carbon black It is related with the said carbon black dispersion liquid by which an agent contains 0.2 mass part or more and 20 mass parts or less.
Formula (A)

  An embodiment of the present invention also relates to a battery electrode mixture layer formed by applying the carbon black dispersion for a battery.

  An embodiment of the present invention is a lithium ion secondary battery comprising a positive electrode having a positive electrode mixture layer on a current collector, a negative electrode having a negative electrode mixture layer on the current collector, and an electrolyte containing lithium. And at least one of a positive electrode and a negative electrode is related with the lithium ion secondary battery which comprises the said battery electrode compound-material layer.

  According to the present invention, it is possible to obtain a carbon black dispersion for a battery having significantly better storage stability and excellent coating properties than when a conventionally known polymer type dispersant is used alone, As a result, it is possible to maintain good coating suitability even after long-term storage.

  In addition, when an electrode mixture layer for a secondary battery is prepared using the dispersion, it is possible to obtain a uniform and good coating film with excellent adhesion to the base material. It is possible to obtain a good and stable coating film even underneath.

  Details of the present invention will be described below. In this specification, “carbon black dispersion”, “carbon black dispersion for battery” is “dispersion”, “N-methyl-2-pyrrolidone” is “NMP”, “polyvinyl acetal or polyvinyl butyral”. “Polyvinyl acetals” and “positive electrode active material or negative electrode active material” may be abbreviated as “electrode 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, ketjen black and the like can be used. Ordinarily oxidized carbon black, graphitized carbon black, carbon nanotubes, carbon nanofibers, and the like can also be used.

  The oxidation treatment of carbon black is performed by treating the carbon black at a high temperature in the air or by treating it with nitric acid, nitrogen dioxide, ozone, etc., for example, phenol group, quinone group, carboxyl group, carbonyl group. This is a treatment for 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 for the production of the dispersion is preferably 0.01 to 1 μm, particularly the average primary particle size range of the carbon black used for general dispersions and paints. -0.2 micrometer is preferable and 0.01-0.1 micrometer is further more preferable. The average primary particle size referred to here indicates an arithmetic average particle size measured with an electron microscope, and this physical property value is generally used to represent the physical characteristics of carbon black.

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

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 industrially produced carbon black such as acetylene black and furnace black is preferably used.

<Dispersant>
In the present invention, one or more polymers selected from the group consisting of polyvinyl alcohol, polyvinyl acetal, polyvinyl butyral, and polyvinyl formal are used as the dispersant.

<Polyvinyl alcohol>
In the present invention, polyvinyl alcohol is used as one embodiment of the dispersant. That is, polyvinyl alcohol is used as a dispersant rather than as a binder. Although there is no restriction | limiting in particular about the manufacturing method of the polyvinyl alcohol used by this invention, Hereinafter, the polyvinyl alcohol obtained by saponifying this from polyvinyl acetate is described.
In general, polyvinyl alcohol is obtained by using polyvinyl acetate obtained by polymerizing vinyl acetate as a raw material, saponifying the polyvinyl acetate, and substituting the acetyl group with a hydroxyl group. Due to this synthesis process, polyvinyl alcohol has an acetyl group and a hydroxyl group, and the ratio is expressed as the degree of saponification.

  In addition, the saponification degree in this invention represents the ratio (mol%) of the repeating unit represented by general formula (A) contained in polyvinyl alcohol. For example, in the case of polyvinyl alcohol obtained by saponifying polyvinyl acetate, the number of hydroxyl groups derived from the vinyl alcohol skeleton contained in the polyvinyl alcohol, the number of acetyl groups derived from the vinyl acetate skeleton and the number of hydroxyl groups derived from the vinyl alcohol skeleton The value divided by the sum of

  The polyvinyl alcohol used in the present invention is exclusively polyvinyl alcohol obtained by saponifying polyvinyl ester, particularly polyvinyl acetate, but is not limited thereto. Moreover, the ratio of the repeating unit represented by the general formula (A) contained in the polyvinyl alcohol is preferably 40 to 99 mol%, more preferably 50 to 95 mol%, and further preferably 55 to 92 mol%. Preferably, 55 to 85 mol% is more preferable, and 60 to 85 mol% is particularly preferably used. If it is polyvinyl alcohol in the said range, various commercial products and synthetic products can be used individually or in combination of 2 or more types.

  In addition, as functional groups other than hydroxyl groups and acetyl groups, for example, those introduced with acetoacetyl group, sulfonic acid group, carboxyl group, carbonyl group, amino group, isocyanate group, those modified with various salts, etc. Anion or cation-modified, unsaturated-modified, acetal-modified (butyral-modified, acetoacetal-modified, formal-modified, etc.) with aldehydes, diol structure, etc. are used in the present invention. These are included in the range of polyvinyl alcohol, and these can be used alone or in combination of two or more.

  Polyvinyl alcohol as a dispersant preferably has an average degree of polymerization of 50 to 3000, more preferably 100 to 3000, still more preferably 100 to 2000, and particularly preferably 100 to 1500. If it is polyvinyl alcohol of the said polymerization degree, various commercial products and synthetic products can be used individually or in combination of 2 or more types.

  Examples of the commercially available polyvinyl alcohol contained in the polyvinyl alcohol include Kuraray Poval (polyvinyl alcohol manufactured by Kuraray Co., Ltd.), Gohsenol (polyvinyl alcohol manufactured by Nippon Synthetic Chemical Industry Co., Ltd.), Denkapoval (manufactured by Denki Kagaku Kogyo Co., Ltd.), J- Various grades can be obtained from the market under trade names such as POVAL (Nippon Vinegar-Poval).

  More specifically, Kuraray Poval PVA-403 (degree of saponification of 78.5 to 81.5 mol%, average degree of polymerization of 300, 4% aqueous solution viscosity at 20 ° C. according to JIS K6726 2.8 to 3.3 mPa · s ), Kuraray Poval PVA-505 (degree of saponification 72.5-74.5 mol%, average polymerization degree 500, 4% aqueous solution viscosity 4.2-5.0 mPa · s), Kuraray Poval L-8, Kuraray Poval L-9 Kuraraypoval L-9-78, Kuraraypoval L-10, Kuraraypoval C-506, Kuraraypoval KL-506, Gohsenol KL-03 (78.5-82.0 mol%, average polymerization degree 500 or less, 4% Aqueous solution viscosity 2.8-3.4 mPa · s), KL-05 (78.5-82.0 mol%, average polymerization degree 1000 or less, 4% aqueous solution viscosity 4.0) 5.0 mPa · s), NK-05R (71.0-75.0 mol%, average polymerization degree 1000 or less, 4% aqueous solution viscosity 4.5-5.5 mPa · s), KP-08R (71.0) -73.5 mol%, average polymerization degree 1000 or less, 4% aqueous solution viscosity 6.0-8.0 mPa · s) and the like, but are not limited thereto.

<Polyvinyl acetals and polyvinyl formal>
In the present invention, polyvinyl acetals or polyvinyl formal is used as another embodiment of the dispersant. That is, polyvinyl acetals or polyvinyl formal is used as a dispersant rather than as a binder. Although there is no restriction | limiting in particular about the manufacturing method of the polyvinyl acetal or polyvinyl formal used by this invention, Hereinafter, it describes about the polyvinyl acetal or polyvinyl formal obtained by using polyvinyl alcohol as a raw material and acetalizing or formalizing this. To do.

  In general, polyvinyl acetals or polyvinyl formal is obtained by reacting polyvinyl alcohol with an aldehyde to acetalize or formalize. For this synthesis process, polyvinyl acetals have an acetyl group, a hydroxyl group, and an acetal group, and polyvinyl formal has an acetyl group, a hydroxyl group, and a formal group. These properties as a polymer are mainly characterized by the ratio of hydroxyl group to acetal group or formal group.

  The polyvinyl acetals and polyvinyl formal used in the present invention are those synthesized by a conventionally known synthesis method, and various commercially available products and synthetic products can be used alone or in combination of two or more. It is not limited to this.

  Examples of functional groups other than hydroxyl group, acetyl group, acetal group or formal group include those introduced with acetoacetyl group, sulfonic acid group, carboxyl group, carbonyl group, amino group, isocyanate group, ether, ester, etc. Those having a structure, those modified with various salts, those modified with other anions or cations are also included in the range of the polyvinyl acetals or polyvinyl formal used in the present invention, and these may be used alone or in combination of two or more. Can be used together.

  15-40 mol% is preferable and, as for the ratio of the repeating unit represented by general formula (A) contained in polyvinyl acetals, 20-36 mol% is more preferable. Moreover, 15 mol% or less is preferable, as for the ratio of the vinyl ester group derived from polyvinyl ester contained in polyvinyl acetals, 10 mol% or less is more preferable, and 5 mol% or less is more preferable.

  5-40 mol% is preferable and, as for the ratio of the repeating unit represented by general formula (A) contained in polyvinyl formal, 10-30 mol% is more preferable.

  The polyvinyl acetals and polyvinyl formal as the dispersant are preferably those having an average calculated molecular weight of 5,000 to 200,000, particularly preferably 10,000 to 150,000, and more preferably 15,000 to 150,000.

Examples of commercially available polyvinyl acetals and polyvinyl formal include various grades under trade names such as eslek (polyvinyl acetal manufactured by Sekisui Chemical Co., Ltd.), mobital (polyvinyl butyral manufactured by Kuraray Co., Ltd.), and vinylec (polyvinyl formal manufactured by JNC). Can be obtained from the market.
More specifically, for example, ESREC BL-1, ESREC BL-10, ESREC BX-L, MOVITAL B16H, MOVITAL 30T, MOBITAL 30HH, MOVITAL 60T, VINYREC K, VINYREC L, VINYREC H, VINYREC E, etc. However, it is not limited to these.

In the present invention, at least one polymer selected from the group consisting of polyvinyl alcohol, polyvinyl acetal, polyvinyl butyral, and polyvinyl formal is used as the dispersant, and the dispersant is preferably polyvinyl alcohol or polyvinyl butyral. Particularly preferred is polyvinyl alcohol.
By using these dispersants, carbon black can be favorably dispersed.

<Acid compound>
In the present invention, an acidic compound is used. There is no restriction | limiting in particular about the acidic compound used by this invention, It can use individually or in combination of 2 or more types irrespective of a commercial item and a synthetic product. In addition, an acidic compound represents the compound which acts as an acid relatively with respect to the electrode active material to be used.

  The acidic compound used in the present invention is preferably an organic acid or a 1,3-diketone, and has at least one acidic functional group selected from the group consisting of a carboxyl group, a sulfonic acid group, a phosphoric acid group, and a thiol group. It is more preferably an organic acid or 1,3-diketone having an organic acid or 1,3-diketone having one or more acidic functional groups selected from the group consisting of a carboxyl group and a sulfonic acid group. More preferred is an organic acid having a carboxyl group or a sulfonic acid group, and an organic acid having a sulfonic acid group is particularly preferred.

  The acid dissociation constant (pKa) of the acidic compound is preferably −5 or more and 10 or less, more preferably −3 or more and 9 or less, further preferably −3 or more and 7 or less, and −3 or more, Those of 5 or less are more preferred, those of -3 or more and 3 or less are more preferred, and those of 1 or more and 3 or less are particularly preferred. The value of the acid dissociation constant is obtained from a chemical handbook as a value in an aqueous solution at 25 ° C. When the value of the acid dissociation constant is too large, the expected effect may not be obtained. On the other hand, when the value is too small, the production line may be corroded or handled with care.

  The molecular weight of the acidic compound is preferably 30 or more and 15000 or less, more preferably 30 or more and 10,000 or less, still more preferably 30 or more and 1000 or less, still more preferably 30 or more and 500 or less, and 30 More preferred are those from 300 to 300, and particularly preferred are from 60 to 200. When the molecular weight is too large, it functions as an aggregating agent for carbon black and active material particles, and the viscosity and storage stability of the dispersion may deteriorate.

  When the acidic compound is a low molecular compound having a molecular weight of 1,000 or less, the number of acidic groups in one molecule is preferably 1 or more and 3 or less, and more preferably 1 or more and 2 or less.

  The acidic compound is preferably soluble in the carbon black dispersion, and is 0.1 part by mass with respect to 100 parts by mass of N-methyl-2-pyrrolidone at 0 to 40 ° C. under atmospheric pressure. It is more preferable to dissolve the above.

  Specific examples of acidic compounds used in the present invention include saturated fatty acids such as acetic acid, propionic acid, caprylic acid and stearic acid, unsaturated carboxylic acids such as oleic acid and sorbic acid, tartaric acid, citric acid and glyceric acid. Aromatic carboxylic acids such as hydroxy acid, benzoic acid, salicylic acid and phthalic acid, dicarboxylic acids such as oxalic acid, succinic acid, adipic acid and maleic acid, and carboxylic acids such as acetic anhydride, benzoic anhydride, phthalic anhydride and maleic anhydride Acid anhydrides, sulfonic acids such as benzenesulfonic acid and toluenesulfonic acid, 1,3-diketones such as acetylacetone, inorganic acids such as hydrochloric acid, sulfuric acid, nitric acid and phosphoric acid, other oxo acid compounds, compounds having a thiol group, phosphorus Examples include compounds having acid groups, phenols, enols, derivatives of these compounds, polymers, etc. It is, but not limited thereto.

<Binder>
The carbon black dispersion of the present invention further contains a binder. As binders 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, fluorine resin; carboxymethylcellulose Such cellulose resins; rubbers such as styrene-butadiene rubber and fluororubber; and conductive resins such as polyaniline and polyacetylene. Moreover, the modified body and mixture of these resin, and a copolymer may be sufficient. In particular, it is preferable to use a polymer compound having a fluorine atom in the molecule, for example, polyvinylidene fluoride, polyvinyl fluoride, tetrafluoroethylene, etc. from the viewpoint of resistance.

  Further, 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. When the molecular weight is small, the resistance and adhesion of the binder may be lowered. When the molecular weight is increased, the resistance and adhesiveness of the binder are improved, but the viscosity of the binder itself is increased and workability is lowered, and the dispersed particles may be remarkably aggregated while acting as an aggregating agent.

In view of industrial applicability assumed by the present invention, the binder preferably contains a polymer compound having a fluorine atom, preferably a polymer compound having a fluorine atom, and is a vinylidene fluoride copolymer. More preferably, it is particularly preferably polyvinylidene fluoride.
Industrially, these binders are mainly used in order to obtain excellent resistance. However, since these are resins with low adhesiveness, they have poor adhesion to the base material when applied to coatings and processing. In many cases, it becomes difficult, and in addition, in the presence of a basic metal oxide, the viscosity may greatly increase, which may cause a problem in storage stability. Therefore, there is a demand for a carbon black dispersion liquid that maintains good adhesion and storage stability while using a vinylidene fluoride copolymer or polyvinylidene fluoride as a binder.

<N-methyl-2-pyrrolidone>
NMP is used for manufacturing electrodes of lithium ion secondary batteries. In the present invention, one or more other solvents may be used in combination as long as the effect of the dispersant and the battery performance are not impaired. However, NMP is used alone because of industrial applicability assumed by the present invention. Is preferred.

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

The positive electrode active material for the lithium ion secondary battery is not particularly limited, but 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 transition metal oxides such as Fe, Co, Ni, and Mn, composite oxides with lithium, and inorganic compounds such as transition metal sulfides. Specifically, transition metal oxide powders such as MnO, V ₂ O ₅ , V ₆ O ₁₃ , TiO ₂ , layered structure lithium nickelate, lithium cobaltate, lithium manganate, spinel structure lithium manganate, etc. Examples thereof include composite oxide powders of lithium and transition metals, lithium iron phosphate materials that are phosphate compounds having an olivine structure, and transition metal sulfide powders such as TiS ₂ and FeS. In addition, conductive polymers such as polyaniline, polyacetylene, polypyrrole, and polythiophene can also be used. Moreover, you may mix and use said inorganic compound and organic compound.

The negative electrode active material for the lithium ion secondary battery is not particularly limited as long as it can be doped or intercalated with lithium ions. For example, metal Li, alloys thereof such as tin alloys, silicon alloys, 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 thereof include carbonaceous powders such as graphite, carbon black, mesophase carbon black, resin-fired carbon materials, air-growth carbon fibers, and carbon fibers. These negative electrode active materials can be used alone or in combination.

  The electrode active material used in the present invention is preferably basic 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 is preferably an active material containing lithium and a metal element other than lithium as a main constituent, 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, or Mn, and lithium containing any of Al, Co, Ni, and Mn. Is more preferable, and a composite oxide with lithium containing Ni and / or Mn is particularly preferable. When these active materials are used, particularly good effects can be obtained.

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 as used herein is an average value of particle diameters of the active material measured with an electron microscope.

<Method for producing carbon black dispersion>
In the dispersion of the present invention, one or more polymers selected from the group consisting of polyvinyl alcohol, polyvinyl acetal, polyvinyl butyral, and polyvinyl formal are used as dispersants, and carbon black is added to NMP using an acidic compound as an additive. It is distributed. In this case, the dispersant and carbon black are added simultaneously or sequentially and mixed to disperse the dispersant while acting (adsorbing) on the carbon black. However, in order to more easily produce a carbon black dispersion, the dispersant is dissolved, swollen, or dispersed in NMP, and then the carbon black is added to the liquid and mixed to disperse the dispersant in carbon. It is more preferable to act (adsorb) on black. Note that the timing of adding the acidic compound may be before the dispersion treatment of carbon black or after the dispersion treatment. Further, a dispersing agent, an acidic compound, carbon black, and an electrode active material may be simultaneously charged into NMP to perform a dispersion treatment.

  As the dispersion device, a disperser usually used for pigment dispersion or the like can be used. For example, mixers such as dispersers, homomixers, planetary mixers, homogenizers (such as “Clairemix” manufactured by M Technique, “Fillmix” manufactured by PRIMIX, “Abramix” manufactured by Silverson, etc.), etc., paint conditioners ( Red Devil), colloid mill ("PUC colloid mill" manufactured by PUC, "colloid mill MK" manufactured by IKA), cone mill ("Cone mill MKO" manufactured by IKA), ball mill, sand mill (Shinmaru Enterprises) "Dynomill", etc.), Attritor, Pearl Mill ("DCP Mill" manufactured by Eirich), Coball Mill and other media type dispersers, 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, the case where a dispersion is produced after the surface treatment of carbon black with a dispersant by dry treatment will be described. A carbon black dispersion can be obtained by adding and mixing a mixture of carbon black and dispersant obtained by the following dry treatment in NMP. Examples of a method for obtaining carbon black surface-treated with a dispersant include a dry treatment method.

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

  Moreover, you may add an organic solvent in the range by which a processed material does not become a gel form at this time. It is expected that the interaction between the carbon black and the dispersant is promoted by improving the wetting or (partly) dissolution of the dispersant by the addition of the solvent and the wetting of the carbon black with respect to the dispersant. The solvent used at this time is not particularly limited. However, when a solvent other than NMP is used, it is desirable to dry after the treatment. Moreover, although the addition amount of an organic solvent changes with materials to be used, it is 0.5-100 mass% with respect to the addition amount of a dispersing agent. Further, the inside of the dry processing apparatus may be treated as 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 lump treated product can be obtained. The obtained processed product may be further dried and pulverized.

  In the present invention, the amount of the solid content with respect to the carbon black dispersion for batteries is preferably 1% by mass to 90% by mass, more preferably 40% by mass to 85% by mass with respect to 100% by mass of the carbon black dispersion for batteries. 55 mass% to 85 mass% is more preferable, and 60 mass% to 85 mass% is particularly preferable.

  In the present invention, the addition amount of polyvinyl alcohol, polyvinyl acetal, polyvinyl butyral, and polyvinyl formal as a dispersant for carbon black is preferably 0.2 parts by mass or more and 50 parts by mass or less with respect to 100 parts by mass of carbon black. 0.2 parts by mass or more and 40 parts by mass or less are more preferable, 0.2 parts by mass or more and 20 parts by mass or less are more preferable, 0.2 parts by mass or more and 10 parts by mass or less are more preferable, and 0.2 parts by mass As mentioned above, 8 mass parts or less are more preferable, 0.3 mass part or more and 6 mass parts or less are further more preferable, and 1 mass part or more and 6 mass parts or less are especially preferable.

  In the present invention, the addition amount of the acidic compound with respect to the carbon black is preferably 0.1 parts by mass or more and 20 parts by mass or less, more preferably 0.1 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the carbon black. Preferably, 0.1 part by mass or more and 5 parts by mass or less are more preferable, 0.1 part by mass or more and 3 parts by mass or less are more preferable, 0.2 part by mass or more and 2 parts by mass or less are more preferable, 0.2 Particularly preferred is 1 part by mass or more.

  The addition amount of the dispersant and the acidic compound in the carbon black dispersion is determined by the specific surface area of the carbon black to be added, the average particle diameter after dispersion of the carbon black particles, the adsorption amount to the carbon black, and the like.

  In the present invention, the amount of the binder added is preferably 0.5 parts by mass or more and less than 20 parts by mass with respect to 100 parts by mass of the positive electrode active material or the negative electrode active material contained in the carbon black dispersion for batteries. As mentioned above, 15 mass parts or less are more preferable, 1 mass part or more and 10 mass parts or less are more preferable, 2 mass parts or more and 8 mass parts or less are further more preferable, and 2 mass parts or more and 5 mass parts or less are especially preferable.

In the present invention, the total amount of polyvinyl alcohol, polyvinyl acetal, polyvinyl butyral, polyvinyl formal, and acidic compound as a dispersant is 100 parts by mass of the positive electrode active material or the negative electrode active material contained in the carbon black dispersion for the battery. 0.05 parts by mass or more and 2.5 parts by mass or less are preferable, 0.05 parts by mass or more and 2 parts by mass or less are more preferable, 0.05 parts by mass or more and 1.5 parts by mass or less are more preferable, and 0 0.05 parts by mass or more and 1.25 parts by mass or less are more preferable, 0.05 parts by mass or more and 1 part by mass or less are more preferable, and 0.05 parts by mass or more and 0.5 parts by mass or less are particularly preferable.
If the amount of the dispersant and / or the acidic compound relative to the positive electrode active material or the negative electrode active material is too large, not only will the relative solid content ratio occupied by the active material or the conductive agent decrease, The acidic compound may elute or swell with respect to the electrolytic solution, and the chemical stability and physical shape stability as the battery electrode mixture layer may deteriorate.

  In the present invention, the addition amount of polyvinyl alcohol, polyvinyl acetal, polyvinyl butyral, or polyvinyl formal as a dispersant is 0.04 with respect to 100 parts by mass of the positive electrode active material or the negative electrode active material contained in the carbon black dispersion for a battery. More than mass part and less than 2 mass parts are preferable, 0.04 mass part or more and less than 1.5 mass parts are more preferable, 0.04 mass part or more and less than 1.25 mass parts are more preferable, 0.04 mass part As mentioned above, less than 1 mass part is further more preferable, 0.04 mass part or more and less than 0.5 mass part are further more preferable, and 0.04 mass part or more and less than 0.3 mass part are especially preferable.

  In the present invention, the addition amount of the acidic compound is preferably 0.01 parts by mass or more and less than 1 part by mass with respect to 100 parts by mass of the positive electrode active material or the negative electrode active material contained in the carbon black dispersion for batteries. 01 parts by mass or more and less than 0.75 parts by mass are more preferred, 0.01 parts by mass or more and less than 0.5 parts by mass are more preferred, 0.01 parts by mass or more and less than 0.25 parts by mass are more preferred, and 0 It is more preferably 0.01 parts by weight or more and less than 0.15 parts by weight, particularly preferably 0.02 parts by weight or more and less than 0.1 parts by weight.

The addition amount of the acidic compound to the positive electrode active material or the negative electrode active material is not only the number of functional groups and acid strength of the acidic compound, but also the adsorption amount of the acidic compound to the active material particles, the particle diameter of the active material, the specific surface area, and the base of the particle surface It is determined by the strength of the property, the concentration and molecular weight of the binder to be added, the reactivity between the binder and the active material, and the like.
If the amount of the acidic compound relative to the positive electrode active material or the negative electrode active material is too large, the dispersion of the particles is deteriorated, the viscosity of the dispersion liquid is greatly increased, and coating may be difficult. Moreover, the function of the dispersant with respect to carbon black may be inhibited. Furthermore, even if a dispersion having good coatability can be obtained, the adhesion of the coating film to the substrate may be greatly deteriorated and workability may be deteriorated.

  By blending in the above ratio, it becomes possible to improve the storage stability of the carbon black dispersion for batteries, which is a problem to be solved by the present invention, the coating suitability and the adhesion of the coating film to the substrate, It becomes easy to obtain a dispersion having excellent dispersibility, storage stability, coating suitability, and adhesion.

<Electrode>
By coating and drying the carbon black dispersion containing the positive electrode active material or the negative electrode active material of the present invention on a current collector, a battery electrode mixture layer can be formed and an electrode can be obtained.

(Current collector)
The material and shape of the current collector used for the electrode are not particularly limited, and those suitable for various secondary batteries can be appropriately selected. For example, examples of the material for the current collector include metals and alloys such as aluminum, copper, nickel, titanium, and stainless steel. In general, a flat foil is used as the shape, but a roughened surface, a perforated foil, or a mesh current collector can also be used.

  There is no restriction | limiting in particular as a method of apply | coating a mixture slurry and the composition for base layer formation on a collector, A well-known method can be used. Specific examples include die coating method, dip coating method, roll coating method, doctor coating method, knife coating method, spray coating method, gravure coating method, screen printing method or electrostatic coating method, and the like. Examples of methods that can be used include standing drying, blower dryers, hot air dryers, infrared heaters, and far-infrared heaters, but are not particularly limited thereto.

  Moreover, you may perform the rolling process by a lithographic press, a calender roll, etc. after application | coating. The thickness of the electrode mixture layer is generally 1 μm or more and 500 μm or less, preferably 10 μm or more and 300 μm or less.

<Secondary battery>
A secondary battery can be obtained by using the above electrode for at least one of a positive electrode and a negative electrode. Secondary batteries include lithium ion secondary batteries, sodium ion secondary batteries, magnesium secondary batteries, alkaline secondary batteries, lead storage batteries, sodium sulfur secondary batteries, lithium air secondary batteries, etc. In the secondary battery, conventionally known electrolytes, separators, and the like can be used as appropriate.

(Electrolyte)
A case of a lithium ion secondary battery will be described as an example. As the electrolytic solution, an electrolyte containing lithium dissolved in a non-aqueous solvent is used. As electrolytes, LiBF ₄ , LiClO ₄ , LiPF ₆ , LiAsF ₆ , LiSbF ₆ , LiCF ₃ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ , Li (CF ₃ SO ₂ ) ₃ C , LiI, LiBr, LiCl, LiAlCl, LiHF ₂ , LiSCN, or LiBPh _4, but are not limited thereto.

  The non-aqueous solvent is not particularly limited. For example, carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate; γ-butyrolactone, γ-valerolactone, and γ Lactones such as octanoic lactone; tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, 1,2-methoxyethane, 1,2-ethoxyethane, and 1, Glymes such as 2-dibutoxyethane; esters such as methyl formate, methyl acetate, and methyl propionate; sulfoxides such as dimethyl sulfoxide and sulfolane; and nitriles such as acetonitrile. And the like. These solvents may be used alone or in combination of two or more.

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

(Battery structure / configuration)
The structure of the lithium ion secondary battery using the composition of the present invention is not particularly limited, but 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, It can be made into various shapes according to the purpose of use, such as a laminated type.

In the present invention, conventionally known dispersants, resins, additives and the like may be used in combination for the purpose of adjusting the physical properties of the coating film and the like as long as the above-described problems are not affected.
Examples of such a dispersant include conventionally known pigment derivatives, resin-type dispersants, low molecular weight surfactants, and the like. Examples of the resin include polyvinylidene fluoride, polytetrafluoroethylene, polyhexafluoropropylene, polyethylene, polypropylene, polymethyl methacrylate, polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, polyacrylic acid, polyacrylamide, and polyurethane. , Polydimethylsiloxane, epoxy resin, acrylic resin, polyester resin, melamine resin, phenol resin, styrene butadiene rubber and other rubbers, lignin, pectin, gelatin, xanthan gum, welan gum, succinoglycan, cellulosic resin, polyalkylene oxide, Examples include polyvinyl ether, chitins, chitosans, starch and the like. Examples of the additive 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.

<Application of carbon black dispersion for batteries>
As a field of application of the carbon black dispersion liquid of the present invention, it is suitably used for electrodes for lithium ion secondary batteries, electrodes for electric double layer capacitors, electrodes for lithium ion capacitors, and the like.

EXAMPLES Hereinafter, although this invention is demonstrated in detail based on an Example, this invention is not limited to a following example, unless the summary is exceeded. In this example, “part” represents “part by mass”, and “%” represents “% by mass”.
Carbon black (sometimes abbreviated as “CB”), polyvinyl alcohol (sometimes abbreviated as “PVA”), binder, electrode active material and the like used in Examples and Comparative Examples are shown below.

<Carbon black>
# 30 (Mitsubishi Chemical Co., Ltd.): Furnace black, average primary particle size 30 nm, specific surface area 74 m ² / g, hereinafter abbreviated as # 30.
# 5 (Mitsubishi Chemical Co., Ltd.): Furnace black, average primary particle diameter 76 nm, specific surface area 29 m ² / g, hereinafter abbreviated as # 5.
Denka black HS-100 (manufactured by Denki Kagaku Kogyo): acetylene black, average primary particle size 48 nm, specific surface area 39 m ² / g, hereinafter abbreviated as HS-100.
Denka black granular product (manufactured by Denki Kagaku Kogyo Co., Ltd.): Acetylene black, average primary particle size 35 nm, specific surface area 69 m ² / g, hereinafter abbreviated as granular product.
EC-300J (manufactured by Lion Corporation): Ketjen black, average primary particle size 40 nm, specific surface area 800 m ² / g, hereinafter abbreviated as 300J.

(Measurement method of average primary particle size of carbon black)
The average primary particle size (MV) of carbon black was measured (calculated) by the method shown below. A sample for measurement was prepared by adding propylene glycol monomethyl ether acetate to a carbon black powder, adding a small amount of Disperbyk-161 as a resin-type dispersant, and dispersing the mixture in a water bath of an ultrasonic cleaner for 1 minute. This sample was applied to a measurement target, dried, and taken with a transmission electron microscope (transmission electron microscope H-7650, manufactured by Hitachi High-Technologies Corporation) to photograph 100 or more primary particles of carbon black. In the photographed image, an arbitrary 100 carbon black particles are selected, the average value of the minor axis diameter and major axis diameter of the primary particles is defined as the particle diameter (d), and then the individual carbon blacks are obtained. Considering it as a sphere having a diameter (d), the volume (V) of each particle was determined, and this operation was performed on 100 carbon black particles, and the calculation was performed using the following equation (1).

Formula (1) MV = Σ (V · d) / Σ (V)

<Dispersant>
<Polyvinyl alcohol>
Kuraray Poval PVA-405 (manufactured by Kuraray Co., Ltd.): polyvinyl alcohol, saponification degree 82 mol%, average polymerization degree 500, hereinafter abbreviated as PVA1.
Kuraray Poval PVA-505 (manufactured by Kuraray Co., Ltd.): polyvinyl alcohol, saponification degree 73 mol%, average polymerization degree 500, hereinafter abbreviated as PVA2.
-PVA3: Polyvinyl alcohol, saponification degree 92 mol%, average polymerization degree about 500.
-PVA4: Polyvinyl alcohol, saponification degree 60 mol%, average polymerization degree about 500.
The PVA3 and PVA4 are obtained by saponifying polyvinyl acetate with sodium hydroxide by a method known in the industry.

<Polyvinyl acetals>
ESREC BH-3 (manufactured by Sekisui Chemical Co., Ltd.): polyvinyl butyral resin, hydroxyl group 34 mol%, butyralization degree 65 mol%, calculated molecular weight 110000. Hereinafter abbreviated as PVAc.

<Acid compound>
-Benzoic acid: Wako Pure Chemical Industries. Molecular weight 122.
-Adipic acid: Wako Pure Chemical Industries. Molecular weight 146.
・ Succinic acid: manufactured by Tokyo Chemical Industry. Molecular weight 118.
O-phthalic acid: manufactured by Tokyo Chemical Industry. Molecular weight 166.
・ Benzene sulfonic acid: Wako Pure Chemical Industries, Ltd. Molecular weight 158. Hereinafter, it is abbreviated as B1.
・ Sartomer 1000: manufactured by Sartomer. Styrene / maleic anhydride copolymer. Styrene / maleic anhydride = 1/1, molecular weight about 5500. Hereinafter, it is abbreviated as S1.
Isoban-10: Kuraray Co. Isobutylene / maleic anhydride copolymer. Molecular weight about 160000. Hereinafter, abbreviated as I1.
・ Citric acid: Wako Pure Chemical Industries. Molecular weight 192.

<Binder>
KF polymer W1100 (manufactured by Kureha): polyvinylidene fluoride (PVDF), weight average molecular weight of about 280000. Hereinafter, it is abbreviated as # 1100.
KF polymer W7300 (manufactured by Kureha): polyvinylidene fluoride (PVDF), weight average molecular weight of about 1,000,000. Hereinafter, it is abbreviated as PVDF.

<Active material>
Positive electrode active material: ternary active material (LiMn _0.3 Co _0.2 Ni ₀ · 5O ₂ ), average particle diameter 4 μm, specific surface area 1.5 m ² / g, hereinafter abbreviated as MCN.
Negative electrode active material: artificial graphite, average particle size 12 μm, hereinafter abbreviated as graphite.

<Other additives>
-Xanthan gum: manufactured by Wako Pure Chemical Industries. Hereinafter, abbreviated as K1.
-Polyvinylpyrrolidone K-90: manufactured by Tokyo Chemical Industry. Viscosity average molecular weight 630000. Hereinafter, it is abbreviated as K-90.
Surfynol 420: manufactured by Nissin Chemical Industry Co., Ltd. Nonionic surfactant. Hereinafter, this is abbreviated as S420.

<Evaluation of carbon black dispersion for battery>
Evaluation of the carbon black dispersions for batteries obtained in Examples and Comparative Examples was performed by measuring viscosity. Judgment of the quality is: ○: Thickness is sufficiently high and the viscosity can be easily applied (good), Δ: Viscosity that can be easily applied but the thixotropy is not so high (possible), Δ △: Thixotropy is sufficiently high and can be applied, but high viscosity (possible), ×: Viscosity that can be applied but low thixotropy (impossible), XX: Thixogenicity is sufficiently high, but coating The viscosity is so high that it cannot be processed (impossible).
The thixotropy referred to here means a property that the viscosity decreases by stirring and increases by standing, and the value of the following formula (2) is 1.3 or more. The case where the property is sufficiently high ”, 1.1 or more and less than 1.3 is regarded as“ thixotropic property is not so high ”, and the case where it is less than 1.1 is regarded as“ low thixotropic property ”. In addition, those having a viscosity value of 100 Pa · s or higher at a shear rate of 10 s ⁻¹ are “viscosity is so high that they cannot be applied”, and those having a viscosity value of 50 Pa · s or more and less than 100 Pa · s are “coating is possible but viscosity is high”. It was. A coating with a large decrease in viscosity due to stirring is easy to apply, and a coating with a large increase in viscosity when left standing is less likely to cause dripping and spreading of the coating liquid, resulting in a good coating film.

Formula (2) Viscosity value when shear rate is 1 s ^-1 / Viscosity value when shear rate is 10 s ^-1

The viscosity and viscosity were measured immediately after the dispersion was kept at 25 ° C. and sufficiently stirred with a spatula. Specifically, using a rheometer (cone plate type, HAAKE RS-75), using a cone sensor with a diameter of 20 mm and a cone angle of 2 °, a speed control mode, a shear rate of 0.1 s ⁻¹ to 1000 s ⁻ Measurement was carried out over ¹ minute up to ¹ .

  The storage stability was evaluated from the change in liquid properties after the carbon black dispersion was stored at 50 ° C. for 7 days. The change in the liquid property is judged from the ease of stirring when stirring with a spatula and the result of rheometer measurement, and from the degree of change to viscosity and viscosity before being subjected to the storage stability test, ○: no problem (good), Δ: viscosity increased but not gelled (possible), x: gelled (very poor), xx: particles aggregated and the dispersion separated into two layers (extremely Bad).

<Preparation of battery carbon black dispersion>
[Example 1-1]
A glass bottle was charged with 54 parts of NMP, 0.25 part of PVA1, and 0.09 part of benzoic acid, and mixed and dissolved sufficiently. Next, 5 parts of carbon black and 2.5 parts of PVDF were charged and dispersed with a homogenizer for 30 minutes. Thereafter, 92.5 parts of MCN was charged and sufficiently mixed and dispersed with a disper to obtain a carbon black dispersion for a battery. The obtained dispersion had good viscosity and viscosity, and maintained a good state even after the storage stability test.

[Example 1-2 to Example 1-29]
According to the composition shown in Table 1, a battery carbon black dispersion was prepared in the same manner as in Example 1-1. The obtained dispersion had good viscosity and viscosity, and maintained a good state even after the storage stability test.

[Comparative Example 1-1 to Comparative Example 1-4]
According to the composition shown in Table 2, a battery carbon black dispersion was prepared in the same manner as in Example 1-1. Although the obtained dispersion had a viscosity that can be applied immediately after production, the thixotropy was low, and after the storage stability test, the viscosity was too high, making it difficult to apply.
It is clear that the viscosity and storage stability of the dispersion cannot be improved when PVA is used alone as a dispersant or when a nonionic surfactant or thickener is used instead of an acidic compound. It became.

[Comparative Example 1-5 to Comparative Example 1-6]
According to the composition shown in Table 2, a battery carbon black dispersion was prepared in the same manner as in Example 1-1. The obtained dispersion was sufficiently high in thixotropy but difficult to be applied, and the viscosity was high. Further, after the storage stability test, some of the particles were aggregated and the dispersion was separated into two layers.
It was revealed that when the amount of the dispersant and the acidic compound relative to 100 parts by mass of the active material is 3 parts by mass or more and the amount of the acidic compound is 3 parts by mass or more, a good dispersion cannot be obtained.

[Comparative Examples 1-7 to Comparative Example 1-8]
According to the composition shown in Table 2, a battery carbon black dispersion was prepared in the same manner as in Example 1-1. Although the obtained dispersion had a viscosity and viscosity that can be applied and was able to be applied after the storage stability test, the results of the cycle test of the electrode mixture layer described later were extremely poor. It was.

<Preparation of battery electrode composite layer>
Using a doctor blade on an aluminum foil with a carbon black dispersion for a battery after a storage stability test including the positive electrode active material or the negative electrode active material obtained in each of the above Examples and Comparative Examples as a battery electrode mixture liquid After coating, the film was dried at 120 ° C. under reduced pressure for 30 minutes. After drying, a coating film (battery electrode mixture layer) having a film thickness of 100 μm was produced.
The obtained battery electrode mixture layer was evaluated by adhesion (peel strength test) and coating film appearance. The appearance of the coating film was visually: ○: no problem (good), Δ: spotted pattern (possible), x: coarse grain streaking (very bad).
The peel strength was measured by a 180-degree peel test method using a desktop tensile tester (manufactured by Toyo Seiki Seisakusho, Strograph E3). Specifically, a 100 mm × 20 mm double-sided tape (No. 5000NS, manufactured by Nitoms Co., Ltd.) is attached on an acrylic plate, and the produced battery electrode mixture layer is adhered to the other side of the double-sided tape, The peel test was conducted by pulling upward at a constant speed (50 mm / min). The results of the peel strength test are as follows: ◎: No problem (particularly good, peel strength of 1 N / cm or more), ○: No problem (good, peel strength of 500 mN / cm or more), Δ: Peel strength is lower than the case of ○ No problem (possible, peel strength 300 mN / cm or more), Δ △: peel strength is lower than △, but usable (possible, peel strength 100 mN / cm or more), x: weak strength, easy to peel off (very poor) , Peel strength less than 50 mN / cm).

[Example 2-1 to Example 2-23, Comparative Example 2-1 to Comparative Example 2-8]
As the positive electrode mixture liquid, the battery electrode mixture liquids obtained in Example 1-1 to Example 1-23 and Comparative Example 2-1 to Comparative Example 2-8 were used. A composite layer) was prepared. The evaluation results are shown in Table 3.

  From Table 3, the battery electrode mixture layer of Example 2-1 to Example 2-23 has a better coating film appearance than the battery electrode mixture layer of Comparative Example 2-1 to Comparative Example 2-6. Furthermore, it was revealed that the adhesion of the coating film was excellent. In Comparative Example 2-1 to Comparative Example 2-6, since the viscosity of the used electrode mixture solution is too high, coating is difficult, and thus good results cannot be obtained with respect to the coating film appearance and adhesion. It was.

<Assembly of lithium ion secondary battery positive electrode evaluation cell>
[Example 3-1 to Example 3-19, Comparative Example 3-1 to Comparative Example 3-4]
The previously prepared battery electrode mixture liquids (Examples 1-1 to 1-17, Examples 1-22 to 1-23, and Comparative Examples 1-5 to 1-8) (Liquid) was applied onto a 20 μm thick aluminum foil serving as a current collector using a doctor blade, dried by heating at 120 ° C. under reduced pressure, and then rolled with a roller press to obtain a positive electrode having a thickness of 100 μm. A composite layer was prepared. This is a punching working electrode with a diameter of 9 mm, a metallic lithium foil (thickness 0.15 mm) as a counter electrode, and a separator made of a porous polypropylene film (# 2400 manufactured by Celgard) is inserted and laminated between the working electrode and the counter electrode, An electrolyte solution (nonaqueous electrolyte solution in which LiPF ₆ is dissolved at a concentration of 1M in a mixed solvent of ethylene carbonate and diethyl carbonate mixed at a volume ratio of 1: 1) is filled and a bipolar electrode type metal cell (HS manufactured by Hosen Co., Ltd.) Flat cell). The cell was assembled in a glove box substituted with argon gas.

<Characteristic evaluation of lithium ion secondary battery positive electrode>
Using the charging / discharging device (SM-8 manufactured by Hokuto Denko Co., Ltd.) at 30 ° C., the produced positive electrode evaluation cell was fully charged with constant current and constant voltage charging (upper limit voltage 4.2 V) at a charging rate of 1.0 C. The charge / discharge for discharging to the discharge lower limit voltage of 3.0 V at a constant current at the same rate as the charge 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 charge / discharge. . The cell after evaluation was disassembled in a glove box substituted with argon gas, and the appearance of the electrode coating film (the coating film appearance after 50 cycles) was visually confirmed. The evaluation criteria for the appearance of the coating film are ○ (very good) when no peeling from the current collector is observed and no change in the appearance, △ (good) when no change is observed in the appearance. The case where the composite material was partially peeled off from the current collector was defined as x (defect).
Further, the capacity retention ratio is a percentage of the discharge capacity at the 50th cycle with respect to the discharge capacity at the 1st cycle, and the closer the value is to 100%, the better. ◎ (very good) when the capacity maintenance ratio is 95% or more, ◯ (good) when the capacity maintenance ratio is 90% or more and less than 95%, and △ (possible when the capacity maintenance ratio is 80% or more and less than 90% In the case where a normal charge / discharge curve could not be obtained due to peeling of the coating film from the current collector, short-circuiting, or the like, and the capacity could not be obtained, it was set to no value (−). The evaluation results are shown in Table 4.

From Table 4, Example 3-1 to Example 3-19 using the electrode of the present invention were compared with Comparative Example 3-1 to Comparative Example 3-4 to maintain the coating film appearance and capacity after 50 cycles. The rate was also good. On the other hand, since Comparative Example 3-1 to Comparative Example 3-2 could not obtain a good coating film, the positive electrode characteristics could not be evaluated. Although Comparative Example 3-3 and Comparative Example 3-4 were able to obtain a coating film, PVAc or PVA was dissolved or greatly swollen in the electrolyte during the cycle test, so that the positive electrode characteristics could be evaluated. There wasn't.
When the amount of the dispersant relative to 100 parts by mass of the active material is 3 parts by mass or more, or when all of the fluorine-containing polymer compound is replaced with PVA or PVAc, it becomes clear that a good battery electrode mixture layer cannot be obtained. It was.

Claims (9)

  A carbon black dispersion comprising carbon black, a binder, an acidic compound, a dispersant, a positive electrode active material or a negative electrode active material, and N-methyl-2-pyrrolidone, wherein the binder has at least a fluorine atom. The molecular compound is included, and the dispersant is at least one polymer selected from the group consisting of polyvinyl alcohol, polyvinyl acetal, polyvinyl butyral, and polyvinyl formal, and further, with respect to 100 parts by mass of the positive electrode active material or the negative electrode active material, A carbon black dispersion for a battery, wherein the total amount of the dispersant and the acidic compound is 0.05 parts by mass or more and 2.5 parts by mass or less.   The carbon for batteries according to claim 1, wherein the polymer compound having fluorine atoms with respect to 100 parts by mass of the positive electrode active material or the negative electrode active material is contained in an amount of 0.5 parts by mass or more and less than 20 parts by mass. Black dispersion.   3. The carbon black dispersion for a battery according to claim 1, wherein the dispersant is contained in an amount of 0.04 parts by mass or more and less than 2 parts by mass with respect to 100 parts by mass of the positive electrode active material or the negative electrode active material.   The carbon black dispersion for a battery according to any one of claims 1 to 3, wherein the acidic compound is contained in an amount of 0.01 parts by mass or more and less than 1 part by mass with respect to 100 parts by mass of the positive electrode active material or the negative electrode active material. liquid.   The acidic compound is an organic acid or 1,3-diketone having one or more acidic functional groups selected from the group consisting of a carboxyl group, a sulfonic acid group, a phosphoric acid group and a thiol group, The carbon black dispersion liquid according to claim 1.   The carbon black dispersion according to any one of claims 1 to 5, wherein the acidic compound has one or two acidic functional groups in the molecule and has a molecular weight of 1000 or less. The dispersant is polyvinyl alcohol containing 50 to 95 mol% of a repeating unit represented by the following general formula (A) in the polymer chain, and the dispersant is 0.2 parts by mass or more with respect to 100 parts by mass of carbon black, 20 The carbon black dispersion according to any one of claims 1 to 6, wherein the carbon black dispersion is contained in an amount of not more than part by mass.
Formula (A)

  A battery electrode mixture layer formed by applying the carbon black dispersion for a battery according to claim 1.   A lithium ion secondary battery comprising a positive electrode having a positive electrode mixture layer on a current collector, a negative electrode having a negative electrode mixture layer on the current collector, and an electrolyte containing lithium, wherein the positive electrode and the negative electrode are at least One is a lithium ion secondary battery comprising the battery electrode mixture layer according to claim 8.