JP2014120410A - Composition for secondary battery electrode formation, secondary battery electrode, and secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a composition for secondary battery electrode formation for forming a secondary battery excellent in charge and discharge cycle characteristics and excellent in dispersibility of an active material and a conductive assistance agent.SOLUTION: The composition for secondary battery electrode formation contains: at least one of an electrode active material (A) or a carbon material (B) which is a conductive assistance agent; an amphoteric resin type dispersant (C) formed by neutralizing with a basic compound at least part of a phosphate group or a sulfo group in a copolymer having aromatic series, a sulfo group or a phosphate group and an amino group; and an aqueous liquid medium (D).

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 conductive additive in the composite ink and the dispersion state of the conductive aid in the composition for forming the underlayer are determined by the distribution state of the active material and conductive aid in the mixture layer and the underlayer. This is because it is related to the distribution state of the conductive auxiliary agent, affects the physical properties of the electrode, and thus affects 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.

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 to provide an electrode forming composition for forming a secondary battery having excellent charge / discharge cycle characteristics, and an electrode forming composition having excellent dispersibility of an active material and a conductive additive. is there.

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 (C).
That is, the present invention relates to a sulfo group or a phosphate group in a copolymer obtained by copolymerizing at least one of the electrode active material (A) or the carbon material (B) which is a conductive assistant and the following monomer. The present invention relates to a composition for forming a secondary battery electrode, comprising an amphoteric resin dispersant (C) obtained by neutralizing at least a part with a basic compound and an aqueous liquid medium (D).
Aromatic ethylenically unsaturated monomer (c1): 5 to 70% by weight
Ethylenically unsaturated monomer (c2) having a sulfo group or a phosphate group: 10 to 70% by weight
Ethylenically unsaturated monomer having an amino group (c3): 1 to 80% by weight
Other monomers (c4) other than (c1) to (c3): 0 to 79% by weight
(However, the total of (c1) to (c4) 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 the amphoteric resin dispersant, the dispersibility of the carbon material as the active material and the conductive auxiliary agent was improved, and 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 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, the fact that the dispersion state of the active material and the conductive additive affects the battery performance is described in detail in the background art section.
The amphoteric resin dispersant (C) relaxes the aggregation of the active material and functions as a dispersant for the carbon material that is a conductive aid.
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 (C) in the present invention will be described.
The amphoteric resin dispersant (C) in the present invention comprises an aromatic ethylenically unsaturated monomer (c1), an ethylenically unsaturated monomer (c2) having a sulfo group or a phosphate group, amino In this copolymer, at least a part of the sulfo group or phosphate group in the copolymer containing the ethylenically unsaturated monomer (c3) having a group as an essential component is neutralized with a basic compound.

First, the ethylenically unsaturated monomer (c1) having an aromatic ring will be described.
Examples of the ethylenically unsaturated monomer (c1) having an aromatic ring used in the present invention include styrene, α-methylstyrene, and benzyl (meth) acrylate.

  Next, the ethylenically unsaturated compound (c2) having a sulfo group and a phosphate group will be described. A monomer having a sulfo group, a phosphate group, or an alkali metal salt, alkaline earth metal salt, or ammonium salt thereof can be used.

  Examples of the monomer having a sulfo group include vinyl sulfonic acid, (meth) allyl sulfonic acid, styrene sulfonic acid, (meth) acryloyloxyethyl sulfonic acid, isoprene sulfonic acid, 2- (meth) acrylamide-2-methylpropane sulfone. Examples include acid and allyloxybenzene sulfonic acid.

Monomers having a phosphoric acid group include mono (2-acryloyloxyethyl) acid phosphate, mono (2-methacryloyloxyethyl) acid phosphate, diphenyl (2-acryloyloxyethyl) phosphate, diphenyl (2-methacryloyloxyethyl). ) Phosphate, phenyl (2-acryloyloxyethyl) phosphate, acid phosphooxyethyl methacrylate, methacryloyl oxyethyl acid phosphate monoethanolamine salt, 3-chloro-2-acid phosphooxypropyl methacrylate, acid phosphooxypoly Oxyethylene glycol monomethacrylate, acid phosphooxypolyoxypropylene glycol methacrylate, (meth) acryloyloxyethyl Cyd phosphate, (meth) acryloyloxypropyl acid phosphate, (meth) acryloyloxy-2-hydroxypropyl acid phosphate, (meth) acryloyloxy-3-hydroxypropyl acid phosphate, (meth) acryloyloxy-3-chloro-2- Examples thereof include hydroxypropyl acid phosphate, allyl alcohol acid phosphate, and the like.

Next, the ethylenically unsaturated monomer (c3) having an amino group will be described.
The ethylenically unsaturated monomer (c3) having an amino group used in the present invention includes dimethylaminoethyl (meth) acrylate, diethylaminoethyl (meth) acrylate, methylethylaminoethyl (meth) acrylate, dimethylaminostyrene, diethylamino Examples include styrene and vinyl pyridine.

Next, the monomer (c4) other than the above (c1) to (c3) 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.

As nitrogen-containing unsaturated compounds, monoalkylol (meth) acrylamides such as (meth) acrylamide, N-methylol (meth) acrylamide, N-methoxymethyl- (meth) acrylamide,
Examples thereof include acrylamide-type unsaturated compounds such as N, N-di (methylol) acrylamide, 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 (C) used in the present invention is such that the total of the monomers (c1) to (c4) is 100% by weight,
5-70% by weight of aromatic ethylenically unsaturated monomer (c1),
10 to 70% by weight of ethylenically unsaturated monomer (c2) having a sulfo group or a phosphate group,
1 to 80% by weight of an ethylenically unsaturated monomer having an amino group (c3),
Other monomers (c4) other than the above (c1) to (c3) are 0 to 79% by weight.
Preferably, (c1): 20 to 70% by weight, (c2): 15 to 60% by weight, (c3): 1 to 70% by weight, and (c4): 0 to 50% by weight.

  The aromatic ring derived from the ethylenically unsaturated monomer (c1) having an aromatic ring, and the amino group derived from the ethylenically unsaturated monomer (c3) having an amino group are an active material (A) or a conductive assistant described later. It is presumed to be the main adsorption site for the agent (B).

The ethylenically unsaturated monomer (c2) having a sulfo group and a phosphate group has a function of dissolving or dispersing a neutralized copolymer in an aqueous liquid medium.
The active material (A) or the conductive additive (B) is adsorbed with the copolymer via an aromatic or amino group, neutralized, and the repulsion of the ionized sulfo group or phosphate group causes the active material ( It is considered that the dispersion state of A) and the conductive auxiliary agent (B) in the aqueous liquid medium can be kept stable.

The molecular weight of the copolymer obtained by copolymerizing the monomers (c1) to (c4) is not particularly limited, but the viscosity of the amphoteric resin dispersant (C) 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 (C) is lower than the predetermined range and the molecular weight of the amphoteric resin dispersant (C) 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 an ethylenically unsaturated monomer (c2) having a sulfo group or a phosphate group, and the composition ratio of the ethylenically unsaturated monomer having a sulfo group or a phosphate 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 20 mgKOH / g to 600 mgKOH / g, and the acid value is preferably in the range of 30 mgKOH / g to 500 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.

  The acid value is a value obtained by converting the acid value (mg KOH / g) measured in accordance with the potentiometric titration method of JIS K 0070 into a solid content.

The amphoteric resin dispersant (C) can be obtained by various production methods.
For example, the monomers (c1) to (c4) are polymerized in an organic solvent that can be azeotroped with water. Thereafter, an aqueous liquid medium typified by water and a neutralizing agent (basic compound) are added to neutralize at least a part of the acidic functional group, the azeotropic solvent is distilled off, and the amphoteric resin dispersant An aqueous solution or dispersion of (C) 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 amine to make it aqueous, and the hydrophilic organic solvent is not distilled off, and the amphoteric resin is added to an aqueous liquid medium containing the hydrophilic organic solvent and water. A liquid in which the mold dispersant (C) 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, various alkaline amines such as ammonia water, various organic amines such as dimethylaminoethanol, diethanolamine, and triethanolamine, and alkali metal hydroxides such as sodium hydroxide, lithium hydroxide, and potassium hydroxide may be used. it can. The copolymer as described above is dispersed or dissolved in an aqueous liquid medium.

<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. There exist positive mix ink or negative mix ink as compound ink, and as already demonstrated, there are various modes as shown in the following (1) to (4), respectively.
(1) A composite ink containing an active material (A), an amphoteric resin type dispersant (C), and an aqueous liquid medium (D).
(2) A composite ink further containing a conductive additive (B) in (1).
(3) A composite ink further containing a binder in (1).
(4) The composite ink further containing the conductive additive (B) and a binder in (1).

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 lithium nickelate, lithium cobaltate, lithium manganate, nickel, cobalt, and manganese Ternary active materials that are composite oxides of lithium and lithium, composite oxide powders of lithium and transition metals such as spinel lithium manganate, lithium iron phosphate materials that are olivine phosphate compounds, TiS ₂ and transition metal sulfide powders such as 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 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.

  Moreover, a conventionally well-known thing can be suitably selected as a positive electrode active material and negative electrode active material for alkaline secondary batteries.

  The size of these 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 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 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., for example, such as phenol group, quinone group, carboxyl group, carbonyl group. 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. (manufactured by Colombian, Furnace Black), # 2350, # 2400B, # 2600B, # 30050B, # 3030B, # 3030B, # 3030B 3350B, # 3400B, # 5400B, etc. (Mitsubishi Chemical Corporation, furnace black), MONARCH1400, 1300, 900, VulcanXC-7 2R, BlackPearls2000, 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 Examples of graphite such as -100, FX-35 (manufactured by Denki Kagaku Kogyo Co., Ltd., acetylene black) include natural graphite such as artificial graphite, flake graphite, lump graphite, and earth graphite, but are not limited thereto. They may be used in combination of two or more.

  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 (D) will be described.
As the aqueous liquid medium (D) 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.

The composite ink may further contain a binder.
The binder in the present invention is used for binding particles such as a conductive additive and other active materials, and the effect of dispersing these particles in a solvent is small.

  Examples of binders include acrylic resins, polyurethane resins, polyester resins, phenol resins, epoxy resins, phenoxy resins, urea resins, melamine resins, alkyd resins, formaldehyde resins, silicone resins, fluororesins, carboxymethylcellulose and other cellulose resins, styrene -Synthetic rubbers such as butadiene rubber and fluorine rubber, conductive resins such as polyaniline and polyacetylene, and the like, and polymer compounds containing fluorine atoms such as polyvinylidene fluoride, polyvinyl fluoride, and tetrafluoroethylene. Further, a modified product, a mixture, or a copolymer of these resins may be used. These binders can be used alone or in combination.

  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 (C) in the solid ink solid content is 0.1 to 15% by weight.
When the conductive auxiliary agent (B) is included, the proportion of the conductive auxiliary agent (B) in the solid ink solid content is preferably 0.1 to 15% by weight.
When the binder is included, the ratio of the binder to the solid material ink solid content is preferably 0.1 to 15% by weight.

Such a composite ink can be obtained by various methods.
The case of the mixed ink of (4) containing an active material (A), a conductive additive (B), an amphoteric resin type dispersant (C), a binder and an aqueous liquid medium (D) will be described as an example.
For example,
(4-1) An aqueous dispersion of an active material containing an active material (A), an amphoteric resin type dispersant (C) and an aqueous liquid medium (D) is obtained, and a conductive additive (B) is added to the aqueous dispersion. A binder ink can be added to obtain a composite ink.
The conductive auxiliary agent (B) and the binder can be added simultaneously, or after the conductive auxiliary agent (B) is added, the binder may be added, or vice versa.
(4-2) An aqueous dispersion of a conductive additive containing the conductive additive (B), the amphoteric resin type dispersant (C) and the aqueous liquid medium (D) is obtained, and an active material (A) is added to the aqueous dispersion. A binder ink 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 binder 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 (C), the binder, and the aqueous liquid medium (D) is obtained, and a conductive auxiliary agent (B ) To obtain a composite ink.
(4-4) An aqueous dispersion of a conductive additive containing a conductive additive (B), an amphoteric resin type dispersant (C) binder, and an aqueous liquid medium (D) is obtained, and an active material (A ) To obtain a composite ink.
(4-5) The active material (A), the conductive additive (B), the amphoteric resin type dispersant (C), the binder, and the aqueous liquid medium (D) can be mixed almost simultaneously to obtain a mixed ink.

(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 (Shinmaru Enterprises "Dynomill", etc.), Attritor, Pearl Mill (Eirich "DCP Mill", etc.), or Coball Mill, etc .; Media type dispersers; 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 underlayer-forming composition contains a conductive additive (B), an amphoteric resin type dispersant (C), and an aqueous liquid medium (D). Furthermore, a binder can also be contained. 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>
Of the composition for forming a secondary battery electrode of the present invention, the composite ink can be applied and dried on a current collector to form a composite layer to 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.
As the shape, a flat plate foil is generally used, but a roughened surface, a perforated foil shape, and a mesh current collector can also be used.

There is no restriction | limiting in particular as a method of apply | coating a mixture ink 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. 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”.

(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 reaction vessel was heated to 110 ° C., and 100.0 parts of styrene, 60.0 parts of 2-acrylamido-2-methylpropylsulfonic acid, 40.0 parts of dimethylaminoethyl methacrylate, and V-601 (manufactured by Wako Pure Chemical Industries, Ltd.) ) 12.0 parts of the mixture was added dropwise over 2 hours to carry out the polymerization reaction. 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. Moreover, the acid value of the copolymer (1) was 73.4 (mgKOH / g).
Further, after cooling to room temperature, 23.3 parts of dimethylaminoethanol was added for neutralization. This is the amount that neutralizes the sulfonic acid 100%. 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.

(Synthesis Examples 2 to 22)
The compounding compositions shown in Table 1 were synthesized in the same manner as in Synthesis Example 1 to obtain dispersants of Synthesis Examples 2-22.

Ｓｔ：スチレン
ＢｚＭＡ：ベンジルメタクリレート
ＡＴＢＳ：２−アクリルアミド−２−メチルプロピルスルホン酸
ＮａＳＳ：４−スチレンスルホン酸ナトリウム
２−ＳＥＭＡ：２−スルホエチルメタクリレート
Ｐ−１Ｍ：２−メタクリロイルオキシエチルアシッドホスフェート（共栄社化学社製）
ＤＭ：ジメチルアミノエチルメタクリレート
ＢＭＡ：ブチルメタクリレート
ＤＭＡＥ：ジメチルアミノエタノール

St: styrene BzMA: benzyl methacrylate ATBS: 2-acrylamido-2-methylpropyl sulfonic acid NaSS: sodium 4-styrene sulfonate 2-SEMA: 2-sulfoethyl methacrylate P-1M: 2-methacryloyloxyethyl acid phosphate (Kyoeisha Chemical) (Made by company)
DM: Dimethylaminoethyl methacrylate BMA: Butyl methacrylate DMAE: Dimethylaminoethanol

[Example 1]
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.

[Example 2]
For a secondary battery electrode, 10 parts of acetylene black (DENKA BLACK HS-100) as a carbon material as a conductive aid, 10 parts of the dispersant described in Synthesis Example (2), and 80 parts of water are placed in a kneader and dispersed. A carbon material dispersion (2) was obtained.

[Examples 3 to 17], [Comparative Examples 1 to 9]
Carbon materials for secondary battery electrodes of Examples 3 to 17 in the same manner as the carbon material dispersion for secondary battery electrodes (1) using the carbon material and the dispersing agent which are conductive assistants shown in Table 2 Dispersions (3) to (17) and carbon material dispersions (18) to (26) for secondary battery electrodes of Comparative Examples 1 to 9 were obtained and dispersed as a carbon material dispersion by the following method. I asked for a degree.

(Determining the degree of dispersion of carbon material dispersion for secondary battery electrode and composite ink)
The degree of dispersion of the carbon material dispersion for the secondary battery electrode and the composite ink was determined by determination with a grind gauge (according to JISK5600-2-5).
The evaluation results are shown in Table 2 for the carbon material dispersion. 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 carbon material dispersion for secondary battery electrodes.

  As shown in Table 2, when the carbon material dispersion for secondary battery electrodes of Examples 1 to 17 of the present invention was used, the carbon material (B), which is a conductive auxiliary agent, was excellent in dispersibility and uniform secondary It became clear that it was a carbon material dispersion for battery electrodes. It can be seen that by using the amphoteric resin type dispersant (C), a uniform carbon material dispersion for a secondary battery electrode excellent in dispersibility can be obtained even if the kind of conductive additive and the kneading method are different.

<Positive electrode mixture ink>, <Positive electrode>, <Coin-type battery>
[Example 18]
With respect to 50 parts of the carbon material dispersion for secondary battery electrodes (1) prepared in Example 1 (5 parts as acetylene black solid content), 45 parts of LiFePO ₄ as a positive electrode active material, binder (polytetrafluoroethylene 30- J: Mitsui / DuPont Fluoro Chemical Co., Ltd., 60% aqueous dispersion) 8.3 parts and 50 parts of water were mixed to prepare a positive electrode material ink for a secondary battery electrode. The dispersity of the composite ink was determined in the same manner as the dispersity of the carbon material dispersion described above.
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 softness | flexibility and adhesiveness were 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 flexibility)
The electrode produced above was formed into a strip shape and wound so that the current collector side was in contact with a metal rod having a diameter of 3 mm, and cracks on the electrode surface that occurred during winding were determined by visual observation. The one that does not crack is more flexible.
○: “No cracks (a level where there is no practical problem)”
○ △: “In rare cases, cracks are seen (there is a problem, but the usable level)”
Δ: “Partial cracks are seen”
×: “Overall cracks are seen”

(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).
When the active material to be used was LiFePO ₄ , constant current charging was continued up to a charge 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, after charging as in the fifth cycle, after storing for 100 hours in a constant temperature bath at 60 ° C., a constant current discharge is performed at a discharge current of 1.2 mA until a discharge end voltage of 2.0 V is 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%.

Further, the active material to be used in the case of LiCoO _2, charging current 1.2 mA, charge end voltage 4.3 V, the discharge current 1.2 mA, except for using discharge end voltage 2.8V, in the case of LiFePO ₄ Similarly, charge / discharge storage characteristics can be measured.
Further, when artificial graphite is used as the active material for the negative electrode (described later), the charge current is 1.5 mA, the charge end voltage is 0.1 V, the discharge current is 1.5 mA, and the discharge end voltage is 2.0 V. As with LiFePO ₄ , charge / discharge storage characteristics can be measured.

[Examples 19 to 28, 30 to 35], [Comparative Examples 10 to 18]
As shown in Table 3, except that the carbon material dispersion for secondary battery electrodes was used, a mixture ink for positive electrode secondary battery electrodes and a positive electrode were obtained and evaluated in the same manner as in Example 18.

[Example 29], [Comparative Examples 19-22]
Carbon for secondary battery electrodes using 45 parts of LiFePO ₄ as a positive electrode active material, 8.3 parts of binder (polytetrafluoroethylene 30-J: manufactured by Mitsui DuPont Fluorochemical Co., Ltd., 60% aqueous dispersion) and 50 parts of water. A positive electrode secondary battery electrode mixture ink and a positive electrode were obtained in the same manner as in Example 18 except that the conductive auxiliary agent and dispersant shown in Table 3 were used instead of the material dispersion, and evaluation was similarly performed. did.

<Preparation of negative electrode for lithium secondary battery>
[Example 36]
With respect to 10 parts of carbon material dispersion for secondary battery electrodes (1) prepared in Example 1 (1 part as acetylene black solid content), 96 parts of artificial graphite as a negative electrode active material, binder (polytetrafluoroethylene 30- J: Mitsui / DuPont Fluoro Chemical Co., Ltd., 60% aqueous dispersion) 5 parts and 90 parts of water were mixed to prepare a secondary battery electrode mixture ink for 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.

[Examples 37 to 40, Comparative Examples 23 to 25]
As shown in Table 3, except that the carbon material dispersion for secondary battery electrodes was used, a mixture ink for negative electrode secondary battery electrodes and a negative electrode were obtained and evaluated in the same manner as in Example 36.

[Example 41], [Comparative Examples 26 and 27]
Dispersion of carbon material for secondary battery electrode using 96 parts of artificial graphite as negative electrode active material, 5 parts of binder (polytetrafluoroethylene 30-J: manufactured by Mitsui DuPont Fluorochemicals Co., Ltd., 60% aqueous dispersion) and 90 parts of water In the same manner as in Example 36 except that the conductive aid and dispersant shown in Table 3 were used instead of using the body, a negative electrode secondary battery electrode mixture ink and a negative electrode were obtained and evaluated in the same manner.

As shown in Table 3, when the ink mixture for secondary battery electrodes of the present invention is used, the carbon material or the active material, which is a conductive auxiliary agent, is uniformly dispersed in the ink mixture. The balance between the property and the adhesiveness is achieved, and also in the battery characteristics, a decrease in discharge capacity after 100 hours at 60 ° C. is suppressed.
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.
In addition, when the dispersion control of the carbon material or the active material that is the conductive auxiliary agent is insufficient, the flexibility and adhesion of the electrode tend to be insufficient. In particular, when the dispersion control of the carbon material that is a conductive additive is insufficient, the tendency is remarkable.
Therefore, when the composite ink for secondary battery electrodes of the present invention is used, the carbon material or the active material as the conductive auxiliary agent is uniformly dispersed in the composite ink, so that the improvement is possible. Conceivable.

[Example 42]
As a positive electrode active material, 45 parts of LiFePO _{4, 5} parts of binder (polytetrafluoroethylene 30-J: manufactured by Mitsui DuPont Fluorochemical Co., Ltd., 60% aqueous dispersion) and 50 parts of water are used, and described in Synthesis Example (1) In the same manner as in Example 18 except that 10 parts (2 parts as a solid content) of the aqueous solution or aqueous dispersion of the amphoteric resin type dispersant (1) was used, a mixture ink for a secondary battery positive electrode and a positive electrode were obtained. Evaluation was performed in the same manner.

[Examples 43 and 44, Comparative Examples 28 and 29]
A mixture ink for a positive electrode of a secondary battery and a positive electrode were obtained in the same manner as in Example 42 except that 2 parts of the dispersant shown in Table 4 or hydroxyethyl cellulose was used, and evaluated in the same manner.

[Example 45]
As the negative electrode active material, 94 parts of artificial graphite, 7 parts of binder (polytetrafluoroethylene 30-J: manufactured by Mitsui DuPont Fluorochemical Co., Ltd., 60% aqueous dispersion) and 90 parts of water were used, and described in Synthesis Example (1). In the same manner as in Example 36 except that 10 parts (2 parts as a solid content) of the aqueous solution or aqueous dispersion of the amphoteric resin type dispersant (1) was used, a composite battery ink for a secondary battery negative electrode and a negative electrode were obtained. Evaluation was performed in the same manner.
[Examples 46 and 47, Comparative Examples 30 and 31]
Except using the dispersing agent shown in Table 4, or 2 parts of hydroxyethyl cellulose, it was carried out similarly to Example 45, and obtained the mixed-material ink for secondary battery negative electrodes, and the negative electrode, and evaluated similarly.

[Example 48]
10 parts of acetylene black (DENKA BLACK HS-100) as a carbon material which is a conductive additive, 5 parts of an aqueous solution or an aqueous dispersion of the amphoteric resin type dispersant (1) described in Synthesis Example (1) (1% as a solid content) Part), binder (polytetrafluoroethylene 30-J: Mitsui DuPont Fluorochemical Co., Ltd., 60% aqueous dispersion) 4 parts, 81 parts of water are mixed in a mixer, and further dispersed in a sand mill. A composition for forming a base layer for a secondary battery electrode 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 mixed material ink for secondary battery positive electrode of Example 35 on the said foundation layer, it dried under reduced pressure heating and obtained the positive electrode similarly to Example 18, and evaluated it similarly.
[Example 49, Comparative Example 32]
Except having used the dispersing agent shown in Table 4, or 1 part of hydroxyethylcellulose, it carried out similarly to Example 48, 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 18, and evaluated it similarly.

As shown in Table 4, when the composition for forming a secondary battery electrode of the present invention was used, as a result of sufficient dispersion control in the composite ink even without the presence of a conductive auxiliary agent, an electrode was obtained. Since the uniform conductive network at the time was formed, it was considered that the flexibility and adhesion of the electrode were balanced, and the battery capacity was also suppressed from lowering the discharge capacity after 60 ° C. and 100 hours. In addition, since no conductive assistant is used, the ratio of the active material contained in the composite ink can be increased, which is thought to lead to an improvement in battery capacity.
Furthermore, when the composition for forming a secondary battery electrode of the present invention is used for the underlayer, it is better than the evaluation results of Example 35 and Comparative Example 11 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 32, 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 49. . 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)

Basically, at least part of the sulfo group or phosphate group in the copolymer obtained by copolymerizing at least one of the electrode active material (A) or the carbon material (B) as a conductive auxiliary agent with the following monomer is basic. The composition for secondary battery electrode formation containing the amphoteric resin type dispersing agent (C) neutralized with a compound, and an aqueous liquid medium (D).
Aromatic ethylenically unsaturated monomer (c1): 5 to 70% by weight
Ethylenically unsaturated monomer (c2) having a sulfo group or a phosphate group: 10 to 70% by weight
Ethylenically unsaturated monomer having an amino group (c3): 1 to 80% by weight
Other monomers (c4) other than (c1) to (c3): 0 to 79% by weight
(However, the total of (c1) to (c4) is 100% by weight)   An electrode for a secondary battery comprising a current collector and at least one of a composite material layer or an electrode underlayer 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.