JP6028286B2 - Emulsion binder for forming secondary battery electrode, mixed ink for forming secondary battery electrode, secondary battery electrode, and secondary battery - Google Patents

Description

The present invention relates to an emulsion binder for forming a secondary battery electrode used in a composite ink used for forming an electrode of a secondary battery.
About.

  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 response to such demands, secondary batteries such as lithium ion secondary batteries and alkaline secondary batteries have been developed, and the development of emulsion binders for forming secondary battery electrodes used to form electrodes is also active. Has been done.

The required performance of the binder used to form the electrode is that the active material and the current collector have good adhesion, the battery reaction is not hindered, and the ionic substance in the electrolyte can be moved as freely as possible without resistance. And so on.
When the electrode is formed when the adhesion between the active material and the current collector is insufficient, the active material may be peeled off from the current collector and the battery characteristics may be deteriorated. On the other hand, when the inhibition of the battery reaction of the resin is large, the internal resistance of the battery is increased, and there is a problem that the performance of the electrode material cannot be sufficiently brought out.

  Therefore, Patent Documents 1 to 3 propose that the binder contains polyethylene glycol or polypropylene glycol in order to reduce the internal resistance of the battery and increase the mobility of the ionic substance.

  Patent Document 4 discloses a binder obtained by copolymerizing an acrylate monomer having an alkylene oxide moiety and a (meth) acrylic acid monomer.

  The secondary battery binders described in Patent Documents 1 to 5 satisfy such requirements as the size and performance of the secondary battery increase and the need for water-based treatment increases in consideration of the environment. I couldn't.

JP 2002-117860 A Japanese Patent No. 2823273 Japanese Patent No. 46669980 Japanese Patent Laid-Open No. 2003-268053

  However, since the resins of Patent Documents 1 to 3 are easily dissolved in the electrolytic solution, there is a problem that the adhesion between the active material and the current collector is insufficient.

  Moreover, since the resin of patent document 4 has a high acid value, it causes oxidative degradation of the resin, and there is a concern about the influence on the battery reaction. Furthermore, since the resin uses an organic solvent, there is a problem that the load on the environment is large.

  The present invention provides a secondary battery capable of forming an electrode having good battery performance because it is difficult to dissolve in an electrolyte solution and thus has good adhesion between an active material and a current collector, and the resin does not hinder the movement of an ionic substance. The object is to provide an electrode forming resin.

In the present invention, the carboxyl group-containing ethylenically unsaturated monomer (A) is 0.1 to 5% by weight, and the ethylenically unsaturated monomer (B) is 0.5 to 20 represented by the following general formula (1). % By weight, (meth) acrylic ethylenically unsaturated monomer secondary amine or (meth) acrylic ethylenically unsaturated monomer tertiary amine- containing monomer (C) 0. The emulsion binder for secondary battery electrode formation which emulsion-polymerized 1-10 weight% and ethylenically unsaturated monomer (D) 65-99.3 weight% copolymerizable with these is made into a structure. Here, the nitrogen-containing units is a concept including in secondary amine or a tertiary amine, a nitrogen-containing bond is a nitrogen-containing group Contact and A phagemid binding an amino group.
Formula _{(1) CH 2 = C (} R 1) -CO-O- (R 2 O) n -R 3
(In the formula, n is an integer of 1 to 50, R ¹ is a hydrogen atom or a methyl group, R ² is an alkylene group having 1 to 3 carbon atoms, and R ³ is a hydrogen atom or an alkyl group having 1 to 10 carbon atoms. Is)

  According to the present invention having the above configuration, the emulsion binder contains alkylene oxide and a nitrogen-containing unit, so that the composite material layer containing the binder has good adhesion to the current collector of the electrode, and the composite material layer By improving the ionic conductivity, the internal resistance of the electrode can be reduced.

  According to the present invention, a secondary battery that can form an electrode that has good adhesion between an active material and a current collector by being hardly dissolved in an electrolyte solution, and that has good battery performance because a resin is less likely to hinder the movement of an ionic material. An emulsion binder for electrode formation could be provided.

The emulsion binder for secondary battery electrode formation of this invention is an emulsion binder which forms secondary battery electrodes other than a nickel-hydrogen secondary battery.
The emulsion binder for forming a secondary battery electrode of the present invention includes a carboxyl group-containing ethylenically unsaturated monomer (A), an ethylenically unsaturated monomer (B) represented by the following general formula (1), and nitrogen-containing A unit-containing monomer (C) and an ethylenically unsaturated monomer (D) copolymerizable therewith are copolymerized in an aqueous medium. And the emulsion binder for secondary battery electrode formation is contained in the mixture ink used for the mixture layer formed in the collector of the electrode of a secondary battery.
Formula _{(1) CH 2 = C (} R 1) -CO-O- (R 2 O) n -R 3
(In the formula, n is an integer of 1 to 50, R ¹ is a hydrogen atom or a methyl group, R ² is an alkylene group having 1 to 3 carbon atoms, and R ³ is a hydrogen atom or an alkyl group having 1 to 10 carbon atoms. Is)

  The carboxyl group-containing ethylenically unsaturated monomer (A) is used to increase the polymerization stability of the emulsion binder. In the monomer (A) used in the present invention, examples of the carboxyl group-containing unsaturated compound include acrylic acid, methacrylic acid, itaconic acid, maleic acid, and 2-methacryloylpropionic acid.

  The amount of the carboxyl group-containing ethylenically unsaturated monomer (A) used is preferably 0.1 to 5% by weight. If it is less than 0.1% by weight, the polymerization stability is low, so that the storage stability of the resulting emulsion binder may be lowered. On the other hand, when the amount is more than 5% by weight, the polymerization stability of the emulsion may be lowered, and the dispersion stability of the resultant composite ink may be lowered.

The acid value of the emulsion binder can be calculated by the type and amount of the carboxyl group-containing ethylenically unsaturated monomer (A). The acid value of the emulsion binder in the present invention can be measured by a JIS K 2501-2003 petroleum product and lubricating oil-neutralization number test method.

  When the acid value is less than 0.1 mg KOH / g, the polymerization stability is low, and thus the storage stability of the resulting emulsion binder may be lowered. On the other hand, when the acid value is larger than 50 mgKOH / g, the polymerization stability of the emulsion is lowered as in the amount of the monomer used, and the dispersion stability of the resulting composite ink may be lowered. Furthermore, the oxidation resistance of the binder is lowered, which may cause battery deterioration.

  The ethylenically unsaturated monomer (B) represented by the general formula (1) is known to have ionic conductivity by having an alkylene oxide moiety. The inventors have improved the ionic conductivity by using an ethylenically unsaturated monomer (B) at a certain ratio, so that the alkylene oxide moiety in the binder has an affinity for the electrolyte, It has been found that an emulsion binder having good adhesion between the active material and the current collector can be obtained.

R ^{2 in the} general formula (1) preferably has 1 to 3 carbon atoms. If the number of carbon atoms in R ² is larger than 4, the hydrophobicity becomes too high and the ionic conductivity may be lowered. R ³ preferably has 1 to 10 carbon atoms. If the number of carbon atoms in R ³ is larger than 10, the hydrophobicity becomes too high and the ionic conductivity may be lowered.
The number of n that is the number of repeating parts of the alkylene oxide moiety is not particularly limited, but is preferably 3 or more. If the number of n is 3 or more and 50 or less, the effect of ion conductivity is further improved, which is preferable.

Specifically, for example, diethylene glycol mono (meth) acrylate, polyethylene glycol mono (meth) acrylate, monoacrylate having a hydroxyl group at the terminal and having a polyoxyalkylene chain, or a corresponding monomethacrylate,
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.

  The amount of the ethylenically unsaturated monomer (B) represented by the general formula (1) is preferably 0.5 to 20% by weight. If the amount is less than 0.5% by weight, the effect of ion conductivity is difficult to obtain because the amount used is small. .

Nitrogen-containing ethylenically unsaturated monomer (C) is (meth) tertiary amines der secondary amine or (meth) acrylic ethylenically unsaturated monomers of the acrylic ethylenically unsaturated monomers The Specifically, N -acryloylmorpholine, N, N- (dimethylamino) ethyl (meth) acrylate, N, N- (dimethylamino) propyl (meth) acrylate, N , N-dimethyl (meth) acrylamide, N, Examples include N-diethyl (meth) acrylamide, N-methyl (meth) acrylamide, N-isopropylacrylamide, N-ethyl (meth) acrylamide, and N-hexyl (meth) acrylamide.

  The amount of the nitrogen atom-containing ethylenically unsaturated monomer (C) used is preferably 0.1 to 10% by weight. If it is less than 0.1% by weight, the polymerization stability is low, so that the storage stability of the resulting emulsion binder may be lowered. On the other hand, when the content is more than 10% by weight, the entanglement between the emulsion particles becomes excessive, the polymerization stability of the emulsion is lowered, and the dispersion stability of the resultant composite ink may be lowered.

The ethylenically unsaturated monomer (D) includes a carboxyl group-containing ethylenically unsaturated monomer (A), an ethylenically unsaturated monomer (B) represented by the general formula (1), and a nitrogen atom-containing ethylene. It is a monomer copolymerizable with the polymerizable unsaturated monomer (C).
Examples of the ethylenically unsaturated monomer (D) include alkyl (meth) acrylates, vinyl group-containing monomers and aromatic ring-containing monomers.
The ethylenically unsaturated monomer (D) is appropriately selected so that the glass transition temperature (hereinafter sometimes abbreviated as Tg) is -40 to 40 ° C. Is preferred.

Specifically, examples of the alkyl-based (meth) acrylate include methyl acrylate (homopolymer glass transition temperature Tg = −8 ° C., hereinafter the same), ethyl acrylate (Tg = −20 ° C.), butyl acrylate ( Acrylic acid esters such as Tg = −45 ° C.) and 2-ethylhexyl acrylate (Tg = −55 ° C.);
Methyl methacrylate (Tg = 100 ° C.), Ethyl methacrylate (Tg = 65 ° C.), Butyl methacrylate (Tg = 20 ° C.), Isobutyl methacrylate (Tg = 67 ° C.), Tertiary butyl methacrylate (Tg = 107 ° C.) ), Methacrylic acid esters such as 2-ethylhexyl methacrylate (Tg = −10 ° C.) and cyclohexyl methacrylate (Tg = 66 ° C.). Examples of the aromatic ring-containing monomer include styrene (glass transition temperature of homopolymer Tg = 100 ° C., hereinafter the same), α-methylstyrene (Tg = 168 ° C.) and benzyl methacrylate. The glass transition temperature of the homopolymer can be measured by reading the intersection of the original baseline and the tangent at the inflection point by DSC.

<Composite ink>
The composite ink for forming a secondary battery electrode of the present invention preferably contains an active material, an emulsion binder, and an aqueous liquid medium.

The positive electrode active material for the lithium ion secondary battery is not particularly limited, but metal oxides capable of doping or intercalating lithium ions, metal compounds such as metal sulfides, and conductive polymers are used. be able to. Examples thereof include transition metal oxides such as Fe, Co, Ni, and Mn, composite oxides with lithium, and inorganic compounds such as transition metal sulfides. Specifically, transition metal oxide powders such as MnO, V ₂ O ₅ , V ₆ O ₁₃ , TiO ₂ , layered structure lithium nickelate, lithium cobaltate, lithium manganate, spinel structure lithium manganate, etc. Examples thereof include composite oxide powders of lithium and transition metals, lithium iron phosphate materials that are phosphate compounds having an olivine structure, and transition metal sulfide powders such as TiS ₂ and FeS.

  In addition, conductive polymers such as polyaniline, polyacetylene, polypyrrole, and polythiophene can also be used. Moreover, you may mix and use said inorganic compound and organic compound.

  The negative electrode active material for the lithium ion secondary battery is not particularly limited as long as it can be doped or intercalated with lithium ions. For example, metal Li, alloys thereof such as tin alloys, silicon alloys, lead alloys, etc., metal oxides such as lithium titanate, lithium vanadate, lithium siliconate, and conductive such as polyacetylene, poly-p-phenylene, etc. Polymers, soft carbon and hard carbon, amorphous carbonaceous materials, artificial graphite such as highly graphitized carbon materials, carbonaceous powder such as natural graphite, carbon black, mesophase carbon black, resin-fired carbon materials, Examples thereof include carbon-based materials such as air-growth carbon fibers and carbon fibers. These negative electrode active materials can be used alone or in combination.

  The size of these active materials is preferably in the range of 0.05 to 100 μm, and more preferably in the range of 0.1 to 50 μm. And it is preferable that the dispersed particle diameter of the active material 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 that is a conductive aid will be described.
The composite ink for forming a secondary battery electrode of the present invention preferably contains a carbon material as a conductive auxiliary agent in order to further increase the conductivity of the electrode.
The carbon material 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, etc. alone Or two or more types can be used together. 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 carbon black 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 amount of nitrogen adsorbed 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. If 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.

  The average primary particle diameter of carbon black is preferably 0.005 to 1 μm, and particularly preferably 0.01 to 0.2 μm. The primary particle diameter here is obtained by measuring and averaging, for example, the particle diameters of 20 to 100 particles from an image magnified 1,000 to 10,000 times with an electron microscope or the like.

  The dispersed particle diameter of the carbon material in the mixed ink is desirably dispersed in the range of 0.03 μm to 5 μm. A composition having a dispersed particle size of the carbon material of less than 0.03 μm may be difficult to produce. In addition, when a composition having a dispersed particle diameter of the carbon material 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.

  As a dispersant used for dispersing the carbon material, a water-soluble cellulose resin, a water-soluble acrylic resin, a water-soluble styrene / acrylic resin, a water-soluble polyester resin, a water-soluble urethane resin, or the like is used as a dispersion resin. be able to. The dispersed particle size 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. It is measured by a distribution meter, for example, 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 Co., Furnace Black), MONARCH1400, 1300, 900, VulcanXC- 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 medium will be described.
As the aqueous medium used in the present invention, water is preferably used, but a water-soluble solvent can be used, for example, in order to improve the coating property to the current collector, if necessary.

  Water-soluble solvents include alcohols, glycols, cellosolves, amino alcohols, amines, ketones, carboxylic acid amides, phosphoric acid amides, sulfoxides, carboxylic acid esters, phosphoric acid esters, ethers And nitriles may be used, and they may be used in a range 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.

The viscosity of the composite ink is preferably 100 mPa · s or more and 30,000 mPa · s or less. The non-volatile content of the composite ink is preferably 30 to 90% by weight.
The composite ink preferably contains as much active material as possible during compounding. For example, the proportion of the active material in the nonvolatile content of the composite ink is preferably 80% by weight or more and 99% by weight or less. Furthermore, when a carbon material is included, the proportion of the carbon material in the non-volatile content of the composite ink is preferably 0.1 to 15% by weight.

(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 “Clairemix” 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.

<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.

(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. Examples of the material of 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.
Moreover, the shape of the current collector is generally a flat foil, but the surface is roughened, porous foam, perforated foil, and mesh. A 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 to 500 μm, preferably 10 μm to 300 μm.

<Secondary battery>
The secondary battery of the present invention comprises the secondary battery electrode of the present invention on 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 electrolytes, LiBF ₄ , LiClO ₄ , LiPF ₆ , LiAsF ₆ , LiSbF ₆ , LiCF ₃ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ , Li (CF ₃ SO ₂ ) ₃ C , LiI, LiBr, LiCl, LiAlCl, LiHF ₂ , LiSCN, or LiBPh _4, but are not limited thereto.

Although it does not specifically limit as a non-aqueous solvent, For example, 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”.

<Binder synthesis example 1>
1.5 parts of acrylic acid as the carboxyl group-containing ethylenically unsaturated monomer (A), and blemmer PME-1000 (methoxypolyethylene glycol methacrylate (R ² O) _n as the ethylenically unsaturated monomer (B) n = 9, NOF Corporation) 10 parts, nitrogen atom-containing ethylenically unsaturated monomer (C), N, N-diethylacrylamide 1.0 part, ethylenically unsaturated monomer (D), Mixture of 52 parts of methyl methacrylate, 35.5 parts of butyl acrylate, 2.0 parts of Hytenol NF-08 (anionic emulsifier manufactured by Daiichi Kogyo Seiyaku) as an emulsifier, and 53.1 parts of ion-exchanged water Was emulsified with a plate blade to prepare 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 50 mPa · s. When the acid value was measured, the acid value of the binder was 13 mgKOH / g.

<Binder Synthesis Examples 2 to 17>
The composition shown in Table 1 was synthesized in the same manner as in Binder Synthesis Example 1, and binders in Synthesis Examples 2 to 17 were obtained.

Abbreviations in the table are as follows.
AA: Acrylic acid MAA: Methacrylic acid 2HEMA: Hydroxyethyl methacrylate PME-200: (Blenmer PME-200, n = 2 of methoxypolyethylene glycol methacrylate (R ² O) _n , manufactured by NOF Corporation)
ACMO: N-acryloylmorpholine NiPAAm: N-isopropylacrylamide MMA: methyl methacrylate BA: butyl acrylate PEG: polyethylene glycol

<Preparation of positive electrode for lithium ion secondary battery>
[Example 1]
A binder 12.5 obtained in Synthesis Example 1 was prepared by mixing 5 parts of acetylene black (Denka Black HS-100) as a carbon material, 45 parts of LiFePO ₄ as a positive electrode active material, and 1 part of carboxymethyl cellulose as a dispersant using a planetary mixer. Part (5 parts as a solid content) and 50 parts of water were mixed to prepare a composite ink for a secondary battery electrode for a positive electrode.
And after apply | coating the obtained 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-dried under reduced pressure, and was the whole electrode. The thickness was adjusted to 100 μm.
Furthermore, the rolling process by a roll press was performed and the 85-micrometer-thick positive electrode was obtained.

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 electrolyte (ethylene carbonate and diethyl carbonate 1: A coin-type lithium ion battery was prepared from a non-aqueous electrolyte solution in which LiPF ₆ was dissolved at a concentration of 1 M in a mixed solvent mixed at a ratio of 1 (volume ratio). The coin-type lithium ion battery was produced in a glove box substituted with argon gas.

(Adhesion evaluation)
The obtained electrode was cut using a knife with six grid cuts in the vertical and horizontal directions at intervals of 2 mm from the electrode surface to the depth reaching the current collector. 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 (good)”
○ △: “Slightly peelable (can be used)”
×: “Peel off at most parts (cannot be used)”

(Durability evaluation of charge / discharge)
About the obtained coin-type lithium ion battery, charging / discharging measurement was performed using the charging / discharging apparatus (Hokuto Denko Co., Ltd. SM-8).
The battery was charged at a current of 1.2 mA until the battery voltage reached 4.2V. After the voltage reached 4.2V, discharging was performed at a current of 1.2 mA until the voltage reached 2.0V. The charge / discharge cycle is defined as one cycle, and 5 cycles of charge / discharge are repeated. 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, under the same conditions as those up to the fifth cycle, after charging only for the sixth cycle, after storing for 100 hours in a constant temperature bath at 60 ° C., until the discharge final voltage reaches 2.0 V at a discharge current of 1.2 mA. Constant current discharge was performed and the rate of change was calculated (the closer to 100%, the better).
○: “Change rate is 95% or more. Particularly excellent.”
○ △: “Change rate is 90% or more and less than 95%. Can be used.”
Δ: “Change rate is 85% or more and less than 90%. Usable.”
Δ ×: “Change rate is 80% or more.
X: “Change rate is less than 80%.

[Examples 2 to 10], [Comparative Examples 1 to 7]
As shown in Table 2, a positive electrode secondary battery electrode mixture ink and a positive electrode were obtained in the same manner as in Example 1, except that the combination of the active material, the carbon material, and the binder synthesis example was changed. evaluated.

<Preparation of negative electrode for lithium ion secondary battery>
[Example 11]
1 part of acetylene black (DENKA BLACK HS-100) as a carbon material, 1 part of carboxymethylcellulose as a dispersant, and 96 parts of artificial graphite as a negative electrode active material were mixed with a planetary mixer, and the binder 12.5 obtained in Synthesis Example 1 Part (5 parts as a solid content) and 90 parts of water 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 8-9]
As shown in Table 2, in the same manner as in Example 11 except that the combination of the active material, the carbon material, and the binder synthesis example was changed, a negative electrode secondary battery electrode mixture ink and a negative electrode were obtained in the same manner. evaluated.

As shown in Table 2, when the emulsion binder for forming a secondary battery electrode of the present invention is used, it is presumed that the battery reaction rate caused between the active materials is improved because the binder has high ion conduction performance. Furthermore, since the adhesion between the active material and the current collector is good, it is considered that the charge / discharge storage characteristics are improved.
On the other hand, in Comparative Example 1, polyethylene glycol is used as the binder. Although polyethylene glycol is excellent in ionic conductivity, it is presumed that the charge / discharge storage characteristics are deteriorated as a result because the adhesion between the substrate and the current collector is low.
In Comparative Example 2, since the content of the monomer (B) of Binder Synthesis Example 12 used in the composite ink is as small as 0.1 part, it is estimated that the degree of improvement in charge / discharge storage characteristics is low. On the other hand, in Comparative Example 3, since the content of the monomer (B) in Binder Synthesis Example 13 used in the composite ink is as large as 40 parts, the storage stability of the binder is low. As a result, it is considered that the dispersion stability of the resultant composite ink also decreases, the composite layer becomes non-uniform, and the adhesion decreases.
In Comparative Example 4, since the nitrogen atom-containing monomer (C) is not used, it is considered that the polymerization stability of the emulsion binder is lowered, the mixture layer becomes non-uniform, and the adhesion is lowered. Similarly, in Comparative Example 5, it is considered that since the nitrogen atom-containing monomer (C) is present in an excessive amount, the polymerization stability of the emulsion binder is lowered, the mixture layer becomes non-uniform, and the adhesion is lowered.
In Comparative Example 6, the storage stability of the binder obtained is low because it does not contain the carboxyl group-containing monomer (A) of the binder synthesis example 16 used in the composite ink, and the dispersion stability of the composite ink is low. It is considered that the instability is caused, the composite material layer becomes non-uniform, and the adhesion is lowered. Similarly, in Comparative Example 7, since the content of the carboxyl group-containing monomer (A) in Binder Synthesis Example 17 used in the composite ink is excessive, the binder storage stability is low, and the dispersion of the composite ink It is considered that stability is caused, the composite material layer becomes non-uniform, and the adhesion is lowered.
From this, in order to form a battery with good charge / discharge storage characteristics, it is considered that a binder that satisfies both the adhesion between the base material and the current collector and the ion conductivity is necessary.

Claims (8)

An emulsion binder for forming secondary battery electrodes excluding nickel-metal hydride secondary batteries, represented by 0.1 to 5% by weight of a carboxyl group-containing ethylenically unsaturated monomer (A), represented by the following general formula (1) Ethylenically unsaturated monomer (B) 0.5 to 20 wt%, nitrogen atom-containing ethylenically unsaturated monomer (C) 0.1 to 10 wt%, and ethylenically unsaturated copolymerizable therewith An emulsion binder for forming a secondary battery electrode obtained by copolymerizing 65 to 99.3% by weight of a monomer (D) in an aqueous medium , wherein the nitrogen atom-containing ethylenically unsaturated monomer (C) is An emulsion binder for forming a secondary battery electrode, which is a secondary amine of a (meth) acrylic ethylenically unsaturated monomer or a tertiary amine of a (meth) acrylic ethylenically unsaturated monomer .

Formula _{(1) CH 2 = C (} R 1) -CO-O- (R 2 O) n -R 3
(In the formula, n is an integer of 1 to 50, R ¹ is a hydrogen atom or a methyl group, R ² is an alkylene group having 1 to 3 carbon atoms, and R ³ is a hydrogen atom or an alkyl group having 1 to 10 carbon atoms. Is) The secondary amine of the acrylic ethylenically unsaturated monomer is N-isopropyl (meth) acrylamide, and the tertiary amine of the (meth) acrylic ethylenically unsaturated monomer is N, N-diethyl. The emulsion binder for secondary battery electrode formation of Claim 1 which is (meth) acrylamide or N- (meth) acryloyl morpholine. The emulsion binder for secondary battery electrode formation of Claim 1 or 2 whose n in General formula (1) is an integer of 3-50. The emulsion binder for secondary battery electrode formation in any one of Claim 1 thru | or 3 whose acid value is 0.1-50 mgKOH / g. 5. A secondary battery electrode forming composite ink comprising the emulsion battery forming emulsion binder according to any one of claims 1 to 4 , an active material, and an aqueous liquid medium. Furthermore, the mixture ink for secondary battery electrode formation of Claim 5 containing the carbon material which is a conductive support agent. The electrode for secondary batteries formed using the mixed-material ink for secondary battery electrode formation of Claim 5 or 6 . A secondary battery comprising at least the secondary battery electrode according to claim 7 .