JP2013069672A - Composition for secondary battery electrode formation, secondary battery electrode and secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a composition for electrode formation which is used for forming a secondary battery having superior charge/discharge cycle characteristics and which is superior in dispersibility in an active material and a conductive assistant.SOLUTION: A composition for secondary battery electrode formation excluding a nickel hydrogen secondary battery contains: at least one of an electrode active material (A) or a carbon material (B) which is a conductive assistant; a nitrogen-containing acrylic emulsion binder (C); an ampholytic resin type dispersant (D) formed by neutralizing at least a part of a carboxyl group in a copolymer having an aromatic ring, the carboxyl group and an amino group with a basic compound; and an aqueous liquid medium (E).

Description

  The present invention relates to a composition for forming a secondary battery electrode, an electrode obtained using the composition, and a secondary battery obtained using the electrode.

  In recent years, small portable electronic devices such as digital cameras and mobile phones have been widely used. These electronic devices have always been required to minimize the volume and reduce the weight, and the batteries to be mounted are also required to be small, light, and have a large capacity. In addition, in a large-sized secondary battery for use in automobiles or the like, it is desired to realize a large-sized secondary battery instead of a conventional lead storage battery.

  In order to meet such demands, development of secondary batteries such as lithium ion secondary batteries and alkaline secondary batteries, for example, development of composite inks used for forming electrodes has been actively conducted. There is also an interest in a composition for forming an underlayer used for forming an underlayer of a composite material layer.

An important characteristic required for the composite ink used for forming the electrode and the composition for forming the underlayer includes uniformity in which the active material and the conductive assistant are appropriately dispersed.
This is because the dispersion state of the active material and the conductive auxiliary in the composition ink and the underlayer forming composition is the distribution state of the active material and the conductive auxiliary in the composite layer and the distribution state of the conductive auxiliary in the underlayer. This is because it affects the electrode physical properties and consequently the battery performance.
Therefore, dispersion of the active material and the conductive auxiliary agent is an important issue. In particular, carbon materials with excellent electrical conductivity (conducting aids) have a strong cohesive force due to their large structure and specific surface area, and should be uniformly mixed and dispersed, whether in the composite ink or in the composition for forming the underlayer. Is difficult.
And if the dispersibility and particle size control of the carbon material that is the conductive auxiliary agent is insufficient, the internal resistance of the electrode cannot be reduced because a uniform conductive network is not formed, and as a result, the performance of the electrode material is sufficient. The problem of being unable to withdraw.

  Moreover, when not only the conductive assistant but also the dispersion of the active material in the composite ink is insufficient, partial aggregation occurs in the composite layer formed from such a composite ink. In addition, resistance distribution occurs on the electrode due to partial aggregation, current concentration occurs when used as a battery, and problems such as partial heat generation and deterioration may occur.

  In addition, the composite ink and the composition for forming the underlayer are required to have appropriate fluidity to enable coating on the surface of the metal foil functioning as a current collector. Furthermore, in order to form a composite material layer or a base layer having a surface that is as flat as possible and having a uniform thickness, the composite ink or the base layer forming composition is required to have an appropriate viscosity.

  After the formation of the composite layer formed from the composite ink and the composition for forming the base layer, the metal foil as the base material is cut into pieces of a desired size and shape, or punched. It is pulled out. Therefore, the material layer and the base layer are required to have hardness that does not damage and softness that does not crack or peel off by cutting or punching.

In Patent Documents 1 to 4, an active material and a conductive material are mixed, and this mixture is kneaded with a cellulose-based thickener aqueous solution, and then an aqueous binder such as tetrafluoropolyethylene and latex is further added and further kneaded. It is disclosed that a composite ink is obtained. However, these composite inks have a problem that the dispersed state is insufficient and the flexibility is poor, and a desired electrode cannot be produced, so that good battery performance cannot be obtained.
In order to solve these problems, a method of using a dispersant in addition to the conventional material has been developed when preparing a composite ink (see Patent Document 5). A good dispersion state of the ink is insufficient, and a desired electrode and a secondary battery are often not obtained. In particular, a composite ink in which the further dispersibility of the conductive assistant is uniform is desired.

In composite inks using a dispersant, it is generally considered that the active material of the dispersant contributes little to the battery reaction. Rather, it is important that the dispersant does not inhibit the battery reaction of the active material. In particular, the total amount of the dispersant used is not adsorbed by the active material or the conductive aid and contributes to the dispersion, and the dispersant that does not contribute to the dispersion dissolves in the aqueous liquid medium in the mixture ink. When the composite ink is applied to the metal foil to form the composite layer, the dispersant that does not contribute to the dispersion is taken into the binder that forms the continuous layer of the composite layer. If the distribution of the dispersant is biased due to poor solubility, the battery reaction may be hindered and battery deterioration may occur. Therefore, in order to make the distribution state of the dispersant uniform, compatibility with the binder becomes important. When the compatibility with the binder is low, the dispersant tends to be locally biased in the binder, and the concern that the dispersant inhibits the battery reaction increases.

Japanese Patent Laid-Open No. 2-15855 Japanese Patent Laid-Open No. 9-082364 JP 2003-142102 A JP 2010-165493 A JP-T-2006-51679 gazette JP 2011-076910 A

  An object of the present invention is an electrode-forming composition for forming a secondary battery having excellent charge / discharge cycle characteristics, which is excellent in dispersibility of an active material and a conductive additive, and is composed of a dispersant and a binder that form an electrode. It is to provide a composition for forming an electrode having high compatibility.

In the present invention, the dispersibility of the electrode active material (A) and the carbon material (B) as the conductive auxiliary agent can be improved by using the amphoteric resin dispersant (D). Furthermore, by using the nitrogen-containing acrylic emulsion type binder (C), the compatibility with the amphoteric resin type dispersant (D) is improved, and the battery reaction inhibition in the mixture layer derived from the dispersant can be reduced. It is a thing.
That is, this invention is a composition for secondary battery electrode formation except a nickel metal hydride secondary battery, Comprising: Electrode active material (A), nitrogen-containing acrylic emulsion type binder (C), and the following monomer are copolymerized Forming a secondary battery electrode comprising an amphoteric resin dispersant (D) obtained by neutralizing at least a part of carboxyl groups in the copolymer with a basic compound, and an aqueous liquid medium (E) It relates to a composition for use.
Ethylenically unsaturated monomer having an aromatic ring (d1): 5 to 70% by weight
Ethylenically unsaturated monomer having a carboxyl group (d2): 15 to 60% by weight
Ethylenically unsaturated monomer having an amino group (d3): 1 to 80% by weight
Other monomers (d4) other than (d1) to (d3): 0 to 79% by weight
(However, the total of (d1) to (d4) is 100% by weight)

  The present invention also relates to a secondary battery electrode comprising a current collector and at least one layer of a composite material layer or an electrode base layer formed from the composition for forming a secondary battery electrode.

  Furthermore, the present invention relates to a secondary battery comprising a positive electrode, a negative electrode, and an electrolytic solution, wherein at least one of the positive electrode or the negative electrode is the secondary battery electrode.

  By using an amphoteric resin type dispersant, the dispersibility of the carbon material, which is an active material and a conductive auxiliary agent, is improved, and by using a nitrogen-containing emulsion type binder, compatibility with the amphoteric resin type dispersant is improved. Thus, the electrode forming composition of the present invention could be obtained. The composition for forming an electrode of the present invention can form a composite material layer and an underlayer excellent in flexibility and adhesion to a current collector, and can provide a secondary battery excellent in charge / discharge cycle characteristics.

The composition for forming a secondary battery electrode of the present invention is a composition for forming a secondary battery electrode other than a nickel-hydrogen secondary battery.
The electrode for a secondary battery can be obtained by various methods.
For example, on the surface of a current collector such as a metal foil,
(1) an ink-like composition containing an active material and a liquid medium (hereinafter referred to as composite ink),
(2) a mixed ink containing an active material, a conductive additive and a liquid medium;
(3) a mixed ink containing an active material, a binder and a liquid medium;
(4) A mixed ink containing an active material, a conductive additive, a binder, and a liquid medium,
It can be used to form a composite layer and obtain an electrode.

  Alternatively, an underlayer is formed on the surface of the current collector of the metal foil using a composition for forming an underlayer containing a conductive additive and a liquid medium, and the above composite ink (1 ) To (4) or other composite inks to form a composite layer and obtain an electrode.

In any case, it has been described in detail in the background art section that the dispersion state of the active material and the conductive additive and the compatibility between the dispersant and the binder influence the battery performance.
The amphoteric resin type dispersing agent (D) relaxes the aggregation of the active material and functions as a dispersing agent for the carbon material that is a conductive additive.
Therefore, the composition for forming a secondary battery electrode of the present invention can be utilized as a composite ink that requires an active material or a composition for forming an underlayer that does not require an active material.
First, the amphoteric resin type dispersant (D) in the present invention will be described.
The amphoteric resin type dispersant (D) in the present invention comprises an ethylenically unsaturated monomer (d1) having an aromatic ring, an ethylenically unsaturated monomer (d2) having a carboxyl group, and an ethylene having an amino group. Is obtained by neutralizing at least a part of the carboxyl group in the copolymer containing the basic unsaturated monomer (d3) as an essential component with a basic compound.

First, the ethylenically unsaturated monomer (d1) having an aromatic ring will be described.
Examples of the ethylenically unsaturated monomer (d1) having an aromatic ring used in the present invention include styrene, α-methylstyrene, and benzyl (meth) acrylate.

Next, the ethylenically unsaturated compound (d2) having a carboxyl group will be described.
The monomer (d2) used in the present invention is, as a carboxyl group-containing unsaturated compound, maleic acid, fumaric acid, itaconic acid, citraconic acid, or an alkyl or alkenyl monoester thereof, phthalic acid β- (meth) Acryloxyethyl monoester, isophthalic acid β- (meth) acryloxyethyl monoester, terephthalic acid β- (meth) acryloxyethyl monoester, succinic acid β- (meth) acryloxyethyl monoester, acrylic acid, methacrylic acid And crotonic acid, cinnamic acid, and the like. In particular, methacrylic acid and acrylic acid are preferable.

Next, the ethylenically unsaturated monomer (d3) having an amino group will be described.
The ethylenically unsaturated monomer (d3) having an amino group used in the present invention includes dimethylaminoethyl (meth) acrylate, diethylaminoethyl (meth) acrylate, methylethylaminoethyl (meth) acrylate, dimethylaminostyrene, diethylamino Examples include styrene.

Next, the monomer (d4) other than (d1) to (d3) will be described.
Examples of (meth) acrylate compounds include alkyl (meth) acrylates and alkylene glycol (meth) acrylates.

  More specifically, examples of the alkyl-based (meth) acrylate include alkyl (meth) acrylate having 1 to 22 carbon atoms such as methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, and butyl (meth) acrylate. ) When there is an acrylate and the purpose is to adjust the polarity, an alkyl group-containing acrylate having an alkyl group having 2 to 10 carbon atoms, more preferably 2 to 8 carbon atoms, or a corresponding methacrylate is preferable.

Examples of the alkylene glycol (meth) acrylate include diethylene glycol mono (meth) acrylate and polyethylene glycol mono (meth) acrylate, which are monoacrylates having a hydroxyl group at the terminal and having a polyoxyalkylene chain, or corresponding monometas. Acrylate, etc.
Methoxyethylene glycol (meth) acrylate, methoxydiethylene glycol (meth) acrylate, etc., monoacrylate having an alkoxy group at the terminal and having a polyoxyalkylene chain or the corresponding monomethacrylate,
There are polyoxyalkylene-based acrylates having a phenoxy or aryloxy group at the terminal, such as phenoxyethylene glycol (meth) acrylate, or corresponding methacrylates.

  Examples of hydroxyl-containing unsaturated compounds other than the above include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, glycerol mono (meth) acrylate, 4-hydroxyvinylbenzene And so on.

  Examples of the nitrogen-containing unsaturated compound include (meth) acrylamide, N-methylol (meth) acrylamide, monoalkylol (meth) acrylamide such as N-methoxymethyl- (meth) acrylamide, N, N-di (methylol) acrylamide, Examples thereof include acrylamide-type unsaturated compounds such as N-methylol-N-methoxymethyl (meth) acrylamide and dialalkylol (meth) acrylamide such as N, N-di (methoxymethyl) acrylamide.

Furthermore, as other unsaturated compounds, perfluoromethylmethyl (meth) acrylate, perfluoroethylmethyl (meth) acrylate, 2-perfluorobutylethyl (meth) acrylate, 2-perfluorohexylethyl (meth) acrylate, etc. Perfluoroalkyl alkyl (meth) acrylates having a C 1-20 perfluoroalkyl group;
Perfluoroalkyl such as perfluorobutylethylene, perfluorohexylethylene, perfluorooctylethylene, perfluorodecylethylene, and perfluoroalkyl group-containing vinyl monomers such as alkylene, vinyltrichlorosilane, vinyltris (βmethoxyethoxy) silane, vinyl Examples thereof include silanol group-containing vinyl compounds such as triethoxysilane and γ- (meth) acryloxypropyltrimethoxysilane and derivatives thereof, and a plurality of them can be used from these groups.

  Examples of the fatty acid vinyl compound include vinyl acetate, vinyl butyrate, vinyl propionate, vinyl hexanoate, vinyl caprylate, vinyl laurate, vinyl palmitate, and vinyl stearate.

  Examples of the alkyl vinyl ether compound include butyl vinyl ether and ethyl vinyl ether.

  Examples of the α-olefin compound include 1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene and the like.

  Examples of vinyl compounds include allyl compounds such as allyl acetate, allyl alcohol, allylbenzene, and allyl cyanide, vinyl cyanide, vinylcyclohexane, vinyl methyl ketone, styrene, α-methylstyrene, 2-methylstyrene, and chlorostyrene. Can be mentioned.

  Examples of the ethynyl compound include acetylene, ethynylbenzene, ethynyltoluene, 1-ethynyl-1-cyclohexanol and the like. These can be used alone or in combination of two or more.

The ratio of the monomers constituting the copolymer in the amphoteric resin type dispersant (D) used in the present invention is such that the total of the monomers (d1) to (d4) is 100% by weight,
5 to 70% by weight of ethylenically unsaturated monomer (d1) having an aromatic ring,
15 to 60% by weight of ethylenically unsaturated monomer (d2) having a carboxyl group,
1 to 80% by weight of ethylenically unsaturated monomer (d3) having an amino group,
The other monomer (d4) other than (d1) to (d3) is 0 to 79% by weight.
Preferably, (d1): 20 to 70% by weight, (d2): 15 to 45% by weight, (d3): 1 to 70% by weight, (d4): 0 to 50% by weight.
More preferably, they are (d1): 30-70 weight%, (d2): 15-35 weight%, (d3): 1-40 weight%, (d4): 0-40 weight%.

  An active ring (A) or a carbon material, which will be described later, includes an aromatic ring derived from an ethylenically unsaturated monomer (d1) having an aromatic ring and an amino group derived from an ethylenically unsaturated monomer (d3) having an amino group. Presumed to be the main adsorption site to (B).

The ethylenically unsaturated monomer (d2) having a carboxyl group has a function of dissolving or dispersing a neutralized copolymer in an aqueous liquid medium.
Then, the active material (A) or the carbon material (B) is adsorbed via an aromatic ring or an amino group, neutralized, and the charge repulsion of the ionized carboxyl group, the active material (A) or the carbon material. It is considered that the dispersion state of (B) in the aqueous liquid medium can be kept stable.

The molecular weight of the copolymer obtained by copolymerizing the monomers (d1) to (d4) is not particularly limited, but the viscosity of the amphoteric resin dispersant (D) in a 20% solid content aqueous solution is preferably 5 to 100. 000 mPa · s, more preferably 10 to 50,000 mPa · s. When the viscosity of the amphoteric resin dispersant (D) is lower than the predetermined range and the molecular weight of the amphoteric resin dispersant (D) is higher than the predetermined range and the molecular weight of the amphoteric resin dispersant (D) is too high, the electrode active material There is a possibility of causing poor dispersion of (A) or the carbon material (B) which is a conductive additive.
In addition, the viscosity in this invention is the value measured on 25 degreeC conditions using the B-type viscosity meter.

The copolymer is obtained by copolymerizing a carboxyl group-containing unsaturated compound (d2), and it is preferable that the constituent ratio of the monomer having an anionic functional group in the copolymer is represented by the acid value as follows. That is, the acid value of the copolymer used is preferably in the range of 50 mgKOH / g to 400 mgKOH / g, and the acid value is preferably in the range of 80 mgKOH / g to 300 mgKOH / g.
When the acid value of the copolymer used in the present invention is lower than the above range, the dispersion stability of the dispersion tends to decrease and the viscosity tends to increase. Moreover, when the acid value of the copolymer used in the present invention is higher than the above range, the adhesion of the copolymer to the pigment surface tends to decrease, and the storage stability of the dispersion tends to decrease.
In addition, the acid value of the copolymer in the present invention is a value obtained by converting the measured acid value (mgKOH / g) into a solid content according to the potentiometric titration method of JIS K0070.

The amphoteric resin dispersant (D) can be obtained by various production methods.
For example, the monomers (d1) to (d4) are polymerized in an organic solvent that can be azeotroped with water. Thereafter, an aqueous liquid medium represented by water and a neutralizing agent are added to neutralize at least a part of the carboxyl groups, the azeotropic solvent is distilled off, and an aqueous solution of the amphoteric resin type dispersant (D) or An aqueous dispersion can be obtained.
As the organic solvent at the time of polymerization, any solvent that azeotropes with water may be used, but those having high solubility in the copolymer are preferable, and ethanol, 1-propanol, 2-propanol, and 1-butanol are preferable. Preferably 1-butanol.

Alternatively, it is copolymerized in a hydrophilic organic solvent, neutralized by adding water and an amine to make it aqueous, and as described above, the hydrophilic organic solvent is not distilled off, and an aqueous liquid medium containing the hydrophilic organic solvent and water In addition, a solution in which the amphoteric resin dispersant (D) is dissolved or dispersed can be obtained.
In this case, the hydrophilic organic solvent used is preferably one having high solubility in the copolymer, preferably glycol ethers, diols, more preferably (poly) alkylene glycol monoalkyl ethers having 3 to 6 carbon atoms. Alkanediols are good.

The following are mentioned as a neutralizing agent used for neutralization of a copolymer.
For example, inorganic alkaline agents such as ammonia water, various organic amines such as dimethylaminoethanol, diethanolamine, and triethanolamine, alkali metal hydroxides such as sodium hydroxide, lithium hydroxide, and potassium hydroxide, organic acids and mineral acids Etc. can be used. The copolymer as described above is dispersed or dissolved in an aqueous liquid medium.

  Next, the nitrogen-containing acrylic emulsion type binder (C) will be described. The binder in the present invention is used to bind particles such as conductive additives and other active materials, and to adhere to a metal foil current collector, and to disperse and stabilize these particles in a solvent. The effect to make is small. Examples of the binder form include a water-soluble type, an emulsion type, and a hydrosol type. Among these, an emulsion type is preferable from the viewpoint of adhesion to the metal foil current collector. The emulsion type here refers to a state in which the binder is not dissolved in the aqueous liquid solvent but is dispersed in the form of particles in the aqueous liquid solvent.

  The compatibility with the dispersant will be described. The dispersant contains amino groups in the copolymer. This amino group and the nitrogen-containing component in the binder are thought to contribute greatly to the compatibility. The present inventors create a binder using a nitrogen atom-containing component, so that when a composite ink is applied to a metal foil and a composition for forming an underlayer is formed on a metal foil, a dispersant and a binder are used. It has been found that the dispersant is uniformly incorporated into the binder forming the continuous layer of the composite material layer and the underlayer without any unevenness, and as a result, the battery characteristics are improved. The nitrogen atom-containing component here refers to at least one of an ethylenically unsaturated monomer, an emulsifier, and an initiator of the binder synthesis material.

Nitrogen-containing ethylenically unsaturated monomers include maleimide, N-vinylpyrrolidone, (
(Meth) acrylic ethylenically unsaturated monomer primary amine, secondary amine, tertiary amine, quaternary ammonium salt, and (meth) acrylamide. Specifically, N-cyclohexylmaleimide, N-phenylmaleimide, N-acryloylmorpholine, N, N- (dimethylamino) ethyl (meth) acrylate, N
, N- (dimethylamino) propyl (meth) acrylate, 3- (3-pyridinyl) propyl (meth) acrylate, N, N-dimethyl (meth) acrylamide, N, N-diethyl (meth) acrylamide, N-methyl ( And (meth) acrylamide, N-isopropylacrylamide, N-ethyl (meth) acrylamide, and N-hexyl (meth) acrylamide. Among these, N-acryloylmorpholine, maleimide, and N-isopropylacrylamide are preferable from the viewpoint of ease of synthesis. These at least one nitrogen-containing ethylenically unsaturated monomer and other ethylenically unsaturated monomers can be used in combination.

  As the ethylenically unsaturated monomer that can be used in combination with the nitrogen-containing ethylenically unsaturated monomer, a known monomer can be used. For example, alkyl (meth) acrylate, alkylene glycol ( Examples include meth) acrylate and styrene.

As nitrogen-containing emulsifiers, long-chain primary amine salts such as RNH ₂ · HCl, RNH ₂ · CH ₃ COOH,
Quaternary ammonium salts such as alkyltrimethylammonium salt, dialkyldimethylammonium salt, alkyldimethylbenzylammonium salt,
Heterocyclic amines such as alkylimidazolines, 1-hydroxyethyl-2-alkylimidazolines, 1-acetylaminoethyl-2-alkylimidazolines, 2-alkyl-4-methyl-4-hydroxymethyloxazolines,
Examples thereof include amine derivatives such as polyoxyethylene alkylamine, N-alkylpropylenediamine, N-alkylpolyethylenepolyamine, N-alkylpolyethylenepolyamine dimethyl sulfate, alkylbiguanide, and long-chain amine oxide. These at least one nitrogen-containing emulsifier and other emulsifiers can be used in combination.

  As an emulsifier that can be used in combination with a nitrogen-containing emulsifier, a known emulsifier can be used, and examples thereof include an anionic emulsifier and a nonionic emulsifier.

  As the nitrogen-containing initiator, 2,2′-azobis (2-amidinopropane) dihydrochloride (V-50 manufactured by Wako), 2,2′azobis (N, N′-dimethyleneisobutylamidine) dihydrochloride (VA−) 044). These at least one nitrogen-containing initiator and other initiators can be used in combination.

  As the initiator that can be used in combination with the nitrogen-containing initiator, a known initiator can be used, and examples thereof include persulfates such as potassium persulfate, ammonium persulfate, and sodium persulfate.

  The nitrogen-containing acrylic emulsion type binder (C) can be prepared by using at least one of a nitrogen-containing ethylenically unsaturated monomer, an emulsifier, and an initiator. Among these, an ethylenically unsaturated monomer is preferable because it has a high ratio as a component constituting the binder and can introduce many nitrogen atoms. In that case, a nitrogen-containing ethylenically unsaturated monomer and the above-mentioned known emulsifier and initiator not containing nitrogen can be used in combination.

The nitrogen-containing acrylic emulsion binder (C) can be obtained by copolymerizing a nitrogen-containing ethylenically unsaturated monomer and another ethylenically unsaturated monomer. The amount of the nitrogen-containing ethylenically unsaturated monomer is preferably from 0.1 to 20% by weight, more preferably from 0.5 to 10% by weight, based on the total amount of the ethylenically unsaturated monomer. If it is less than 0.1% by weight, there is a concern that the effect of improving the compatibility with the dispersant is not sufficiently exhibited. When the amount is more than 20% by weight, the dispersion stability is lowered, and there is a concern that the dispersion stability may be lowered during preparation of the composite ink.

  The nitrogen-containing acrylic emulsion-type binder (C) can be prepared by a polymerization method such as emulsion polymerization, suspension polymerization, miniemulsion polymerization, or dispersion polymerization. Among these, emulsion polymerization is preferable from the viewpoint of easy progress of the polymerization reaction.

  The ratio of the solid content of the nitrogen-containing acrylic emulsion binder (C) to the total solid content of the composite ink is preferably 0.1 to 15% by weight, and more preferably 1 to 10% by weight.

<Composite ink>
As described above, the composition for forming a secondary battery electrode of the present invention can be used as a mixture ink or a composition for forming an underlayer. Therefore, a description will be given of a composite ink that essentially includes an active material, which is one of the preferred embodiments of the composition for forming a secondary battery electrode of the present invention. The composite ink includes a positive electrode composite ink or a negative electrode composite ink. The composite ink includes an electrode active material (A), a nitrogen-containing acrylic emulsion binder (C), and an amphoteric resin dispersant (D). Further, a carbon material (B) made of an aqueous liquid medium (E) and further being a conductive auxiliary agent can be used.

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, transition metal sulfide powders such as TiS ₂ and FeS, and the like.
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 alloy, silicon alloy, lead alloy, 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 size of these electrode active materials (A) is preferably in the range of 0.05 to 100 μm, and more preferably in the range of 0.1 to 50 μm. And it is preferable that the dispersed particle diameter of the electrode active material (A) in compound-material ink is 0.5-20 micrometers. The dispersed particle size referred to here is a particle size (D50) that is 50% when the volume ratio of the particles is integrated from the fine particle size distribution in the volume particle size distribution. A particle size distribution meter such as a dynamic light scattering type particle size distribution meter ("Microtrack UPA" manufactured by Nikkiso Co., Ltd.).

Next, the carbon material (B) which is a conductive support agent will be described.
The composite ink for forming a secondary battery electrode of the present invention preferably contains a carbon material (B) in order to further increase the conductivity of the formed electrode.
The carbon material (B), which is a conductive aid in the present invention, is not particularly limited as long as it is a conductive carbon material, but graphite, carbon black, conductive carbon fiber (carbon nanotube, carbon nanofiber) , Carbon fiber), fullerene and the like can be used alone or in combination of two or more. From the viewpoint of conductivity, availability, and cost, it is preferable to use carbon black.

  Carbon black is a furnace black produced by continuously pyrolyzing a gas or liquid raw material in a reactor, especially ketjen black using ethylene heavy oil as a raw material. Channel black that has been rapidly cooled and precipitated, thermal black obtained by periodically repeating combustion and thermal decomposition using gas as a raw material, and particularly various types such as acetylene black using acetylene gas as a raw material, or 2 More than one type can be used in combination. Ordinarily oxidized carbon black, hollow carbon and the like can also be used.

  The oxidation treatment of carbon is performed by treating carbon at a high temperature in the air or by secondary treatment with nitric acid, nitrogen dioxide, ozone, etc. This is a treatment for directly introducing (covalently bonding) an oxygen-containing polar functional group to the carbon surface, and is generally performed to improve the dispersibility of carbon. However, since it is common for the conductivity of carbon to fall, so that the introduction amount of a functional group increases, it is preferable to use the carbon which has not been oxidized.

As the specific surface area of the carbon black used increases, the number of contact points between the carbon black particles increases, which is advantageous in reducing the internal resistance of the electrode. Specifically, the specific surface area (BET) determined from the adsorption amount of nitrogen is 20 m ² / g or more and 1500 m ² / g or less, preferably 50 m ² / g or more and 1500 m ² / g or less, more preferably 100 m ^2. / G or more and 1500 m ² / g or less are desirable. When carbon black having a specific surface area of less than 20 m ² / g is used, it may be difficult to obtain sufficient conductivity, and carbon black of more than 1500 m ² / g may be difficult to obtain from commercially available materials. is there.

  Further, the particle size of the carbon black to be used is preferably 0.005 to 1 μm, particularly preferably 0.01 to 0.2 μm in terms of primary particle size. However, the primary particle diameter here is an average of the particle diameters measured with an electron microscope or the like.

It is desirable that the dispersed particle size in the composite ink of the carbon material (B), which is a conductive additive, be refined to 0.03 μm or more and 5 μm or less. It may be difficult to produce a composition having a dispersed particle size of the carbon material as the conductive aid of less than 0.03 μm. In addition, when a composition having a dispersed particle size of the carbon material as the conductive auxiliary agent exceeding 2 μm is used, there may be problems such as variations in the material distribution of the composite coating film and variations in the resistance distribution of the electrodes. .
The dispersed particle size referred to here is a particle size (D50) that is 50% when the volume ratio of the particles is integrated from the fine particle size distribution in the volume particle size distribution. A particle size distribution meter such as a dynamic light scattering type particle size distribution meter ("Microtrack UPA" manufactured by Nikkiso Co., Ltd.).

Examples of commercially available carbon black include Toka Black # 4300, # 4400, # 4500, # 5500 (Tokai Carbon Co., Furnace Black), Printex L and the like (Degussa Co., Furnace Black), Raven 7000, 5750, 5250, 5000 ULTRA III, 5000 ULTRA, etc., Conductex SC ULTRA
, Conductex 975 ULTRA, etc., PUER BLACK100, 115, 205, etc. (Columbian Co., furnace black), # 2350, # 2400B, # 2600B, # 30050B, # 3030B, # 3230B, # 3350B, # 3400B, # 5400B, etc. (Manufactured by Chemical Co., Furnace Black), MONARCH 1400, 1300, 900, Vulcan XC-72R, Black Pearls 2000, etc. (Cabot, Furnace Black), Ensaco 250G, Ensaco 260G, Ensaco 350G, SuperP-Li (manufactured by TIMCAL), Ketjen Black EC-300J EC-600JD (manufactured by Akzo), Denka Black, Denka Black HS-100, FX-35 (electrochemistry) Examples of graphite such as acetylene black (manufactured by Kogyosha) include natural graphite such as artificial graphite, flake graphite, lump graphite, and earth graphite, but are not limited to these, and two or more kinds are combined. May be used.

  As the conductive carbon fibers, those obtained by firing from petroleum-derived raw materials are preferable, but those obtained by firing from plant-derived raw materials can also be used. For example, VGCF manufactured by Showa Denko Co., Ltd. manufactured with petroleum-derived raw materials can be mentioned.

Next, the aqueous liquid medium (E) will be described.
As the aqueous liquid medium (E) used in the present invention, it is preferable to use water, but if necessary, for example, a liquid medium compatible with water in order to improve the coating property to the current collector. May be used.
Liquid media compatible with water include alcohols, glycols, cellosolves, amino alcohols, amines, ketones, carboxylic acid amides, phosphoric acid amides, sulfoxides, carboxylic acid esters, and phosphoric acid esters , Ethers, nitriles and the like, and may be used as long as they are compatible with water.

  Furthermore, a film forming aid, an antifoaming agent, a leveling agent, a preservative, a pH adjuster, a viscosity adjuster, and the like can be blended in the composite ink as necessary.

Although it depends on the coating method, the viscosity of the composite ink is preferably 100 mPa · s or more and 30,000 mPa · s or less in the range of 30 to 90% by weight of the solid content.
It is preferable that the active material (A) is contained as much as possible within the viscosity range that can be applied. For example, the proportion of the active material (A) in the solid ink solid content is 80 wt% or more and 99 wt% or less. Is preferred.
Moreover, it is preferable that the ratio of the amphoteric resin type dispersant (D) in the solid ink solid content is 0.1 to 15% by weight.
When the carbon material (B) is included, the proportion of the carbon material (B) in the solid material ink solid content is preferably 0.1 to 15% by weight.

The composite ink of the present invention can be obtained by various methods.
However, the use of the carbon material (B) is arbitrary.
For example,
(4-1) An aqueous dispersion of an active material containing an active material (A), an amphoteric resin type dispersant (D), and an aqueous liquid medium (E) is obtained, and the carbon material (B) and A nitrogen-containing acrylic emulsion binder (C) can be added to obtain a composite ink.
The carbon material (B) and the nitrogen-containing acrylic emulsion binder (C) can be added simultaneously, or after the carbon material (B) is added, the binder may be added, or vice versa.
(4-2) Obtaining an aqueous dispersion of the conductive additive containing the carbon material (B), the amphoteric resin type dispersant (D) and the aqueous liquid medium (E), and adding the active material (A) to the aqueous dispersion A nitrogen-containing acrylic emulsion binder (C) can be added to obtain a composite ink.
The active material (A) and the binder can be added simultaneously, or after adding the active material (A), the nitrogen-containing acrylic emulsion type binder (C) may be added, or vice versa.
(4-3) An aqueous dispersion of the active material containing the active material (A), the amphoteric resin type dispersant (D), the nitrogen-containing acrylic emulsion type binder (C), and the aqueous liquid medium (E) is obtained, and the aqueous A carbon material (B) can be added to the dispersion to obtain a mixed ink.
(4-4) Obtaining an aqueous dispersion of a conductive additive containing a carbon material (B), an amphoteric resin type dispersant (D), a nitrogen-containing acrylic emulsion type binder (C), and an aqueous liquid medium (E), An active material (A) can be added to the aqueous dispersion to obtain a composite ink.
(4-5) The active material (A), the carbon material (B), the amphoteric resin type dispersant (D), the nitrogen-containing acrylic emulsion type binder (C), and the aqueous liquid medium (E) are mixed almost simultaneously. Ink can be obtained.

(Disperser / Mixer)
As an apparatus used for obtaining the composite ink, a disperser or a mixer which is usually used for pigment dispersion or the like can be used.
For example, mixers such as dispersers, homomixers, or planetary mixers; homogenizers such as “Clearmix” manufactured by M Technique, or “fillmix” manufactured by PRIMIX; paint conditioner (manufactured by Red Devil), ball mill, sand mill Media type dispersers such as “Dynomill” manufactured by Shinmaru Enterprises, Inc., Attritor, Pearl Mill (“DCP Mill” manufactured by Eirich), or Coball Mill; Media-less dispersers such as “Starburst” manufactured by Machine, “Nanomizer” manufactured by Nanomizer, etc., “Claire SS-5” manufactured by M Technique, or “MICROS” manufactured by Nara Machinery; or other roll mills, etc. Although The present invention is not limited to these. Moreover, as the disperser, it is preferable to use a disperser that has been subjected to a metal contamination prevention treatment from the disperser.

  For example, when using a media-type disperser, a disperser in which the agitator and vessel are made of a ceramic or resin disperser, or the surface of the metal agitator and vessel is treated with tungsten carbide spraying or resin coating. Is preferably used. As the media, it is preferable to use glass beads, ceramic beads such as zirconia beads or alumina beads. Moreover, also when using a roll mill, it is preferable to use a ceramic roll. Only one type of dispersion device may be used, or a plurality of types of devices may be used in combination. Further, in the case of a positive or negative electrode active material in which particles are easily broken or crushed by a strong impact, a medialess disperser such as a roll mill or a homogenizer is preferable to a media type disperser.

<Underlayer forming composition>
As described above, the composition for forming a secondary battery electrode of the present invention can be used not only as a mixture ink but also as a composition for forming an underlayer.
The composition for forming an underlayer contains a conductive additive (B), a nitrogen-containing acrylic emulsion binder (C), an amphoteric resin dispersant (D), and an aqueous liquid medium (E). About each component, it is the same as that of the case of compound ink.
The proportion of the carbon material (B) as a conductive additive in the total solid content of the composition used for the electrode underlayer is preferably 5% by weight or more and 95% by weight or less, and more preferably 10% by weight or more and 90% by weight or less. preferable. If the carbon material (B) as a conductive auxiliary agent is small, the conductivity of the underlayer may not be maintained. On the other hand, if the carbon material (B) as a conductive auxiliary agent is too much, the resistance of the coating film decreases. There is a case. Moreover, although the appropriate viscosity of electrode base layer ink is based on the coating method of electrode base layer ink, generally it is preferable to set it as 10 mPa * s or more and 30,000 mPa * s or less.

<Electrode>
The composite ink of the present invention can be applied and dried on a current collector to form a composite layer and obtain a secondary battery electrode.
Alternatively, the composition for forming an underlayer of the composition for forming a secondary battery electrode of the present invention is formed by forming an underlayer on the current collector, and providing a composite layer on the underlayer, for a secondary battery. An electrode can also be obtained. The composite material layer provided on the base layer may be formed using the above-described composite material inks (1) to (4) of the present invention, or may be formed using other composite material inks.

(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 the case of a lithium ion battery, aluminum is particularly preferable as the positive electrode material, and copper is preferable as the negative electrode material.
In general, foil on a flat plate is used as the shape, but the surface is roughened, porous foam, perforated foil, and mesh current collector. Can also be used.

There is no restriction | limiting in particular as a method of apply | coating mixed-material ink 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. When the underlayer is provided, the total thickness of the underlayer and the composite 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. Conventionally known electrolyte solutions, separators, and the like for secondary batteries 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 the electrolyte, LiBF ₄ , LiClO ₄ , LiPF ₆ , LiAsF ₆ , LiSbF ₆ , LiCF ₃ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ , Li (CF ₃ SO ₂ ) ₃ C , LiI, LiBr, LiCl, LiAlCl , LiHF 2, LiSCN, or LiBPh ₄ etc. but are not limited to.

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

  Furthermore, the electrolyte solution may be a polymer electrolyte that is held in a polymer matrix and made into a gel. 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.

(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.

  EXAMPLES The present invention will be described more specifically with reference to the following examples. However, the following examples do not limit the scope of rights of the present invention. In the examples and comparative examples, “part” represents “part by weight”.

(Dispersant synthesis example 1)
A reaction vessel equipped with a gas introduction tube, a thermometer, a condenser, and a stirrer was charged with 200.0 parts of n-butanol and replaced with nitrogen gas. The inside of the reaction vessel was heated to 110 ° C., and a mixture of 100.0 parts of styrene, 60.0 parts of acrylic acid, 40.0 parts of dimethylaminoethyl methacrylate, and 12.0 parts of V-601 (manufactured by Wako Pure Chemical Industries, Ltd.) The polymerization reaction was carried out dropwise over 2 hours. After completion of the dropwise addition, the mixture was further reacted at 110 ° C. for 3 hours, 0.6 parts of V-601 (manufactured by Wako Pure Chemical Industries, Ltd.) was added, and the reaction was further continued at 110 ° C. for 1 hour to obtain a copolymer (1) solution. Got. The weight average molecular weight of the copolymer (1) was about 10,000, and the acid value was 219.1 (mgKOH / g).
Further, after cooling to room temperature, 74.2 parts of dimethylaminoethanol was added for neutralization. This is the amount that neutralizes 100% of acrylic acid. Furthermore, after adding 400 parts of water and making it aqueous, it heated to 100 degreeC, butanol was azeotroped with water, and butanol was distilled off.
Dilution with water gave an aqueous solution or dispersion of an amphoteric resin dispersant (1) with a nonvolatile content of 20%. Moreover, the viscosity of the aqueous solution of the amphoteric resin type dispersant (1) having a nonvolatile content of 20% was 40 mPa · s.

(Dispersant Synthesis Examples 2 to 12)
The compounding compositions shown in Table 1 were synthesized in the same manner as in Synthesis Example 1 to obtain dispersants of Synthesis Examples 2-12.

St: Styrene AA: Acrylic acid BzMA: Benzyl methacrylate DM: Dimethylaminoethyl methacrylate BMA: Butyl methacrylate

(Carbon material dispersion for secondary battery electrode)
10 parts of acetylene black (Denka Black HS-100) as a carbon material which is a conductive additive, and 10 parts of an aqueous solution or an aqueous dispersion of the amphoteric resin type dispersant (1) described in Synthesis Example (1) (2% as solid content) Part) and 80 parts of water were mixed in a mixer, and further dispersed in a sand mill to obtain a carbon material dispersion (1) for a secondary battery electrode.

[Carbon material dispersion for secondary battery electrode]
Using the dispersant shown in Table 1, carbon material dispersions (2) to (12) for secondary battery electrodes were obtained in the same manner as for the carbon material dispersion (1) for secondary battery electrodes.

<Binder Synthesis Example 13>
As nitrogen-containing monomer, 5.0 parts of N-acryloylmorpholine, as other monomers, 53 parts of methyl methacrylate, 40.5 parts of butyl acrylate, 1.5 parts of acrylic acid, anionic emulsifier as emulsifier Hytenol NF-08 (an anionic emulsifier manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) and a mixture of 53.1 parts of ion-exchanged water were emulsified with a blade to create a monomer pre-emulsion and placed in a dropping tank. .
A reaction vessel is a 2 L four-necked flask equipped with a reflux condenser, a stirrer, a thermometer, a nitrogen inlet tube, and a raw material inlet, and 89.4 parts of ion-exchanged water is introduced into the reaction vessel while introducing nitrogen. The liquid temperature was warmed to 60 ° C. while stirring. Subsequently, 0.2 parts of Haitenol NF-08 as an emulsifier is added to the reaction vessel, and the monomer pre-emulsion is continuously dropped from a dropping tank over 5 hours, using 0.3 part of ammonium persulfate, Emulsion polymerization was performed at 60 ° C. over 6 hours.

After completion of the dropwise addition, the mixture was kept at 60 ° C. for 3 hours for aging. Thereafter, cooling was started, the temperature was lowered to 50 ° C., and the mixture was filtered through a 180 mesh polyester filter cloth to obtain a nitrogen-containing acrylic emulsion binder. There was no aggregate remaining on the filter cloth, and the polymerization stability was good.
A part of the emulsion after filtration was measured, dried at 150 ° C. for 20 minutes, and the nonvolatile content concentration was determined to be 40.0%. The emulsion had a pH of 2.0 and a viscosity of 10 mPa · s.

<Binder synthesis examples 14 to 18>
By the composition shown in Table 2, it synthesize | combined by the method similar to binder synthesis example 13, and the binder of the synthesis examples 14-18 was obtained.

ACMO: N-acryloylmorpholine NIPAAm: N-isopropylacrylamide MMA: methyl methacrylate BA: butyl acrylate

(Compatibility of dispersant and binder)
The compatibility between the dispersant and the binder was evaluated as follows. 25 parts of dispersant (5 parts as solid content) and 12.5 parts of binder (5 parts as solid content) are mixed, applied to a 50 μm PET film, dried at 100 ° C. for 3 minutes, Produced. The thickness of the resin layer of the obtained film was 3 μm. The degree of compatibility of the obtained film was determined by visual judgment. The evaluation criteria are shown below.
Y: “Clear”
Δ: “Slightly cloudy”
×: “Opaque or aggregated”

<Composite ink for lithium ion secondary battery electrode>, <Positive electrode>, <Coin-type battery>
[Example 1]
Carbon fiber dispersion for secondary battery electrode (1) 50 parts (5 parts as acetylene black solid content), 45 parts of LiFePO ₄ as positive electrode active material, 12.5 parts of binder synthesized in Synthesis Example 13 (solid content) 5 parts) and 50 parts of water were mixed to produce a positive electrode material ink for a secondary battery electrode. The degree of dispersion of the composite ink was determined by determination with a grind gauge (according to JISK5600-2-5). The evaluation results are shown in Table 3. The numbers in the table indicate the size of the coarse particles. The smaller the value, the better the dispersibility and the more uniform the ink mixture for secondary battery electrodes.
And after apply | coating this mixed-material ink for secondary battery electrodes for positive electrodes on the 20-micrometer-thick aluminum foil used as a collector using a doctor blade, it heat-drys under reduced pressure and the thickness of an electrode becomes 100 micrometers. Adjusted as follows.
Furthermore, the rolling process by a roll press was performed, the positive electrode from which thickness becomes 85 micrometers was produced, and the adhesiveness was evaluated with the following method.

Next, the obtained positive electrode was punched into a diameter of 16 mm, a working electrode, a metallic lithium foil counter electrode, a separator (porous polypropylene film) inserted between the working electrode and the counter electrode, and an electrolytic solution (ethylene carbonate and diethyl carbonate). A coin-type battery comprising a non-aqueous electrolyte solution in which LiPF ₆ was dissolved at a concentration of 1 M in a mixed solvent obtained by mixing 1: 1 at a volume ratio. The coin-type battery was used in a glove box substituted with argon gas, and a predetermined battery characteristic evaluation was performed after the coin-type battery was produced.

(Electrode adhesion)
Using the knife, the incision from the surface of the electrode to the depth reaching the current collector was cut into 6 grids in the vertical and horizontal directions at intervals of 2 mm. An adhesive tape was applied to the cut and immediately peeled off, and the degree of the active material falling off was determined by visual judgment. The evaluation criteria are shown below.
○: “No peeling (practical level)”
○ △: “Slightly peeled (problem but usable level)”
Δ: “About half peel”
×: “Peeling at most parts”

(Charge / discharge storage characteristics)
About the obtained coin-type battery, charging / discharging measurement was performed using the charging / discharging apparatus (SM-8 by Hokuto Denko).
The constant current charging was continued up to a charging end voltage of 4.2 V at a charging current of 1.2 mA. After the battery voltage reached 4.2 V, constant current discharge was performed at a discharge current of 1.2 mA until the discharge end voltage of 2.0 V was reached. These charge / discharge cycles are defined as one cycle, and 5 cycles of charge / discharge are repeated, and the discharge capacity at the fifth cycle is defined as the initial discharge capacity. (The initial discharge capacity is assumed to be 100% maintenance rate).

Next, the battery was charged in the same way as the 5th cycle, stored in a constant temperature bath at 60 ° C. for 150 hours, and then discharged at a discharge current of 1.2 mA until a discharge end voltage of 2.0 V was reached. (The closer to 100%, the better).
○: “Change rate is 95% or more. Particularly excellent.”
○ △: “Change rate is 90% or more and less than 95%. No problem at all”
Δ: “Change rate is 85% or more and less than 90%.
×: “Change rate is less than 85%.

[Examples 2 to 12], [Comparative Examples 1 to 5]
As shown in Table 3, except that the combination of the carbon material dispersion for the secondary battery electrode and the binder synthesis example was changed, the mixture ink for the positive electrode secondary battery electrode and the positive electrode were obtained in the same manner as in Example 1. Evaluation was performed in the same manner.

[Example 13], [Comparative Example 6]
As in Example 1, except that 45 parts of LiFePO ₄ , a binder shown in Table 3 and 50 parts of water were used as the positive electrode active material, and the dispersant shown in Table 3 was used instead of the carbon material dispersion for secondary battery electrodes. Thus, a mixture ink for positive electrode secondary battery electrode and a positive electrode were obtained and evaluated in the same manner.

<Preparation of negative electrode for lithium ion secondary battery>
[Example 14]
For the carbon material dispersion for secondary battery electrode (1) 10 parts (1 part as acetylene black solid content), 96 parts of artificial graphite as the negative electrode active material, 12.5 parts of binder synthesized in Synthesis Example 13, and water 90 Parts were mixed to prepare a composite ink for a secondary battery electrode for a negative electrode.
This negative electrode mixture ink was applied onto a copper foil having a thickness of 20 μm serving as a current collector using a doctor blade, and then dried by heating under reduced pressure so that the thickness of the electrode was adjusted to 100 μm. A rolling process using a roll press was performed to prepare a negative electrode having a thickness of 85 μm, and evaluation was performed in the same manner as in the case of the positive electrode. The charge / discharge retention characteristics were evaluated using an evaluation coin-type battery having a negative electrode as a working electrode and a metal lithium foil as a counter electrode.

[Comparative Examples 7-8]
As shown in Table 3, except that the combination of the carbon material dispersion for secondary battery electrodes and the binder synthesis example was changed, a mixture ink for negative electrode secondary battery electrodes and a negative electrode were obtained in the same manner as in Example 14, Evaluation was performed in the same manner.

[Example 15], [Comparative Example 9]
In the same manner as in Example 14 except that 96 parts of artificial graphite as a negative electrode active material, a binder shown in Table 3 and 90 parts of water were used, and the dispersant shown in Table 3 was used instead of the dispersion for secondary battery electrodes. A composite ink for a negative electrode for a secondary battery electrode and a negative electrode were obtained and evaluated in the same manner.

(Charge / discharge storage characteristics)
About the obtained coin-type battery, charging / discharging measurement was performed using the charging / discharging apparatus (SM-8 by Hokuto Denko).
The battery was charged to 150% of the calculated battery capacity at a charging current of 0.2C. Thereafter, constant current discharge was performed at a discharge current of 0.2 C until a discharge end voltage of 0.8 V was reached. These charge / discharge cycles are defined as one cycle, and 5 cycles of charge / discharge are repeated, and the discharge capacity at the fifth cycle is defined as the initial discharge capacity. (The initial discharge capacity is assumed to be 100% maintenance rate).

Next, after charging with a charging current of 1 C, constant current discharging is performed with a discharging current of 1 C until the discharge end voltage reaches 0.8 V, and 500 cycles of charging and discharging are performed with these charging and discharging cycles as one cycle. The rate of change was calculated repeatedly (the closer to 100%, the better).
○: “Change rate is 95% or more. Particularly excellent.”
○ △: “Change rate is 90% or more and less than 95%. No problem at all”
Δ: “Change rate is 85% or more and less than 90%.
×: “Change rate is less than 85%.

As shown in Table 3, when the composite battery ink for forming a secondary battery electrode of the present invention is used, the carbon material or the active material, which is a conductive additive, is uniformly dispersed in the composite ink. It is considered that the balance between flexibility and adhesiveness is achieved, and the charge / discharge storage characteristics are also improved in the battery characteristics.
As for this, when the carbon material or active material, which is a conductive auxiliary agent, is not sufficiently dispersed in the mixture ink, a uniform conductive network as an electrode is not formed. It is considered that resistance distribution due to mechanical aggregation occurs, and current concentration occurs when used as a battery, so that deterioration is accelerated.
Moreover, when the dispersion control of the carbon material or the active material which is the conductive auxiliary agent is insufficient, the electrode adhesion tends to be insufficient. In particular, when the dispersion control of the carbon material that is a conductive additive is insufficient, the tendency is remarkable.
Furthermore, it is thought that by improving the compatibility between the dispersant and the binder, inhibition of the battery reaction derived from the dispersant is suppressed in the composite layer, and the battery characteristics are improved. As in Comparative Example 5, even when the dispersion state of the carbon material or the active material, which is a conductive additive, is good, if the compatibility between the dispersant and the binder is low, the binder layer in the continuous layer in the composite layer Thus, the distribution of the dispersant is biased, the resistance is locally increased, the electrode is deteriorated, and the durability of the battery is finally lowered.
On the other hand, as in Comparative Example 1, it is considered that the battery characteristics are deteriorated even though the compatibility is good due to the decrease in the adhesion of the electrodes. Therefore, in order to improve battery characteristics, it is considered necessary to satisfy both electrode adhesion and compatibility. Although there is a correlation between the compatibility and the battery characteristics, it is considered necessary to ensure the adhesion of the electrodes as a precondition.
For this reason, when the composite ink for forming a secondary battery electrode of the present invention is used, the carbon material or the active material, which is a conductive auxiliary agent, is uniformly dispersed in the composite ink, and the phase of the dispersant and the binder is further increased. It is considered that the good solubility makes it possible to reduce the inhibition of the battery reaction of the dispersant and to improve it.

[Example 18]
A secondary battery electrode undercoat layer was prepared by mixing 12.5 parts of binder synthesized in Synthesis Example 13 with 10 parts of carbon material dispersion (1) for secondary battery electrode (1 part as acetylene black solid content). A forming composition was obtained, and the degree of dispersion was measured with a grind gauge.
And after applying this composition for base layer formation on the 20-micrometer-thick aluminum foil used as a collector using a doctor blade, it heat-dried and formed the base layer so that thickness might be set to 8 micrometers.
Subsequently, after applying the mixture ink for secondary battery positive electrode of Example 5 on the said base layer, it dried under reduced pressure heating, obtained the positive electrode similarly to Example 5, and evaluated it similarly.

[Example 19, comparative example 13]
Except having used the carbon material dispersion shown in Table 4, it carried out similarly to Example 18, and obtained the composition for base layer formation for secondary battery electrodes, and evaluated similarly.
Subsequently, after applying the mixture ink for secondary battery positive electrode shown in Table 4 on the said base layer, it dried under reduced pressure heating, obtained the positive electrode similarly to Example 5, and evaluated it similarly.

  As shown in Table 4, when the composition for forming a secondary battery electrode of the present invention is used for the underlayer, it is even better than the evaluation result of Example 5 in which the underlayer is not used. I understand. This is presumably because the composition for forming a secondary battery electrode of the present invention made the contact portion between the current collector and the composite material layer more uniform and strong. However, in Comparative Example 13, the dispersion state of the composition for forming the secondary battery electrode for the underlayer was insufficient, and even when the electrode was used, the result was inferior to the evaluation result of Example 5. . This is presumably because the state of close contact between the current collector and the composite material layer was inadequate, resulting in a non-uniform state as an electrode as compared with the case where the base layer was not used.

Claims (3)

A composition for forming a secondary battery electrode excluding a nickel metal hydride secondary battery,
A carboxyl group in a copolymer obtained by copolymerizing at least one of an electrode active material (A) or a carbon material (B) as a conductive additive, a nitrogen-containing acrylic emulsion binder (C), and the following monomers: A composition for forming a secondary battery electrode, comprising an amphoteric resin type dispersant (D) obtained by neutralizing at least a part of the polymer with a basic compound and an aqueous liquid medium (E).
Ethylenically unsaturated monomer having an aromatic ring (d1): 5 to 70% by weight
Ethylenically unsaturated monomer having a carboxyl group (d2): 15 to 60% by weight
Ethylenically unsaturated monomer having an amino group (d3): 1 to 80% by weight
Other monomers (d4) other than (d1) to (d3): 0 to 79% by weight
(However, the total of (d1) to (d4) is 100% by weight)   An electrode for a secondary battery comprising a current collector and at least one layer of a composite material layer or an electrode base layer formed from the composition for forming a secondary battery electrode according to claim 1.   A secondary battery comprising a positive electrode, a negative electrode, and an electrolyte solution, wherein at least one of the positive electrode or the negative electrode is a secondary battery electrode according to claim 2.