JP2015065141A - Binder for battery electrode, electrode using the same, and battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aqueous binder having a small environmental load in which a coating property of electrode slurry is improved, a binding property is high, and oxidation degradation is especially prevented from occurrence under the electrode environment, and also to provide an electrode using the same, and a battery.SOLUTION: Disclosed is a binder for a battery electrode which contains a polymer containing (A) a (meta) acrylic monomer and a constitutional unit derived from (B) a multifunctional (meta) acrylate monomer, and (C) a silicon-based or mineral oil-based deforming agent. An electrode is prepared using this binder and adopted in a battery such as a lithium ion secondary battery.

Description

  The present invention relates to a binder used for an electrode of a battery, an electrode manufactured using the binder, and a battery manufactured using the electrode. In this specification, the battery includes an electrochemical capacitor and is a primary battery or a secondary battery. Specific examples of the battery are a lithium ion secondary battery and a nickel metal hydride secondary battery.

It is known to use a binder in the battery electrode. A typical example of a battery having an electrode using a binder is a lithium ion secondary battery.
Lithium ion secondary batteries have high energy density and high voltage, and are therefore used in electronic devices such as mobile phones, notebook computers, and camcorders. Recently, due to heightened awareness of environmental protection and the development of related laws, applications as in-vehicle applications such as electric vehicles and hybrid electric vehicles and storage batteries for household power storage are also progressing.

  A lithium ion secondary battery is generally composed of a negative electrode, a positive electrode, a separator, an electrolytic solution, and a current collector. Regarding the electrode, the negative electrode is coated on a current collector typified by copper foil with a negative electrode active material such as graphite or hard carbon capable of inserting and removing lithium ions, a conductive additive, a binder, and a solvent. Obtained by drying. Currently, styrene-butadiene rubber (hereinafter abbreviated as “SBR”) dispersed in water is generally used as a binder.

  On the other hand, the positive electrode is made by mixing a layered positive electrode active material such as lithium cobaltate or spinel type lithium manganate with a conductive auxiliary such as carbon black, a binder such as polyvinylidene fluoride or polytetrafluoroethylene, and the like. The coating liquid dispersed in such a polar solvent is manufactured by applying and drying on a current collector foil represented by an aluminum foil in the same manner as the negative electrode.

  The binder of these lithium ion batteries needs to increase the addition amount of the binder in order to ensure the binding force, and the performance degradation due to this is mentioned as a problem. Further, N-methylpyrrolidone is used as a slurry solvent, and an aqueous binder is desired from the viewpoint of recovery, cost, toxicity and environmental load. However, when an aqueous SBR binder is used, there is a problem that it is oxidized and deteriorated in a positive electrode environment. Therefore, the binder of the positive electrode still uses polyvinylidene fluoride or polytetrafluoroethylene using N-methylpyrrolidone as a dispersion solvent as a binder, and binds the current collector to the active material or between the active materials. There is an urgent need to develop a binder suitable for the production of an electrode for a secondary battery, which is superior in water quality, has a low environmental impact, and has high oxidation resistance.

In order to solve the above problems, Patent Documents 1 and 2 disclose a binder containing a copolymer composed of aromatic vinyl, conjugated diene, ethylenically unsaturated carboxylic acid ester and unsaturated carboxylic acid (Patent Document 1), and A binder comprising a polymer aqueous dispersion selected from styrene-butadiene polymer latex and acrylic emulsion is proposed (Patent Document 2).
Further, in Patent Documents 3 and 4, a binder (Patent Document 3) containing a copolymer composed of aromatic vinyl, conjugated diene, (meth) acrylic acid ester and ethylenically unsaturated carboxylic acid, and bifunctional (meta) ) Binder (Patent Document 4) containing a polymer containing acrylate is proposed.
However, when these binders are used for electrodes (positive electrode and / or negative electrode), the charge / discharge cycle decreases under high temperature conditions. In particular, when used for a positive electrode, there is a concern that there is a problem with oxidation resistance under high voltage conditions, and battery characteristics deteriorate.

JP 2006-66400 A JP 2006-260782 A JP 11-025989 A JP 2001-256980 A

  The present invention has been made in view of the above circumstances, and has a water-based binder with a low environmental load, which has excellent electrode slurry coating properties, high binding properties, and does not cause oxidative degradation in an electrode environment (especially in a positive electrode environment). An object is to provide an electrode and a battery using the same.

As a result of repeated studies to achieve the above object, the present inventors have found that a polymer containing a structural unit derived from a (meth) acrylic monomer and a structural unit derived from a polyfunctional (meth) acrylate monomer, By using a binder containing a silicone-based and / or mineral oil-based antifoaming agent, it has been found that the above problems can be solved, and the present invention has been made. That is, the present invention relates to the following.
[1]
A polymer comprising (A) a (meth) acrylic monomer and (B) a structural unit derived from a polyfunctional (meth) acrylate monomer;
(C) A binder composition for battery electrodes, comprising a silicone-based and / or mineral oil-based antifoaming agent.
[2]
The battery electrode binder composition [3] according to [1], wherein the (meth) acrylic monomer (A) is a (meth) acrylate monomer having a hydroxyl group.
The binder composition for battery electrodes according to [2], wherein the (meth) acrylic monomer having a hydroxyl group is an alkylene glycol mono (meth) acrylate having a molecular weight of 100 to 1,000.
[4]
The binder composition for battery electrodes according to any one of [1] to [3], wherein the polyfunctional (meth) acrylate (B) is a 3-5 functional (meth) acrylate.
[5]
The binder composition for battery electrodes according to any one of [1] to [4], wherein the silicone-based antifoaming agent is dimethylsilicone.
[6]
The binder composition for battery electrodes according to any one of [1] to [5], wherein the battery is a secondary battery.
[7]
A battery electrode comprising the binder composition according to any one of [1] to [6] and an active material.
[8]
[7] A battery comprising the electrode according to [7].

The binder composition of the present invention has good dispersibility of each component at the time of electrode slurry preparation, improves the coating property of the slurry (where the bubbles remain in the coating), and prevents bubbles from remaining on the electrode. it can.
The binder composition of this invention is excellent in binding property with an active material, a conductive support agent, and a current collector. The excellent binding property (strong binding property) is considered to be caused by the large surface area of the polymer fine particles dispersed in water and the use of structural units derived from a monomer having a hydroxyl group. It is done.
The binder composition of the present invention provides an electrode having excellent flexibility.
In the binder composition of the present invention, dissolution in the electrolytic solution is suppressed, and the binder composition does not substantially dissolve in the electrolytic solution. This insolubility is considered to be due to a highly crosslinked structure by using a structural unit derived from a polyfunctional (meth) acrylate monomer as a crosslinking agent component.
The present invention can provide a battery having a high capacity and a long battery life, particularly a secondary battery. The secondary battery is excellent in charge / discharge cycle characteristics. In particular, the secondary battery is excellent in long-term cycle life and cycle charge / discharge characteristics at a high temperature (eg, 60 ° C.).
The secondary battery of the present invention can be used at a high voltage and has excellent heat resistance.
Since the binder composition is water-based (the medium is water), the burden on the environment is small, and no organic solvent recovery device is required.

The binder composition of the present invention comprises a polymer comprising (A) a (meth) acrylic monomer and (B) a structural unit derived from a polyfunctional (meth) acrylate monomer,
(C) A battery electrode binder composition comprising a silicone-based and / or mineral oil-based antifoaming agent.

  Examples of the (meth) acrylic monomer (A) include a (meth) acrylate monomer (A-1) having a hydroxyl group, a (meth) acrylic acid ester monomer (A-2), and a (meth) acrylic acid monomer (A-3). Yes, these can be used alone or in combination of two or more.

  As the (meth) acrylate monomer (A-1) having a hydroxyl group, alkylene glycol mono (meth) acrylate having a molecular weight of 100 to 1000 is preferable. Specific examples include diethylene glycol mono (meth) acrylate, triethylene glycol mono (meth) acrylate, tetraethylene glycol mono (meth) acrylate, polyethylene glycol mono (meth) acrylate, dipropylene glycol mono (meth) acrylate, and tripropylene glycol. Examples thereof include mono (meth) acrylate, tetrapropylene glycol mono (meth) acrylate, and polypropylene glycol mono (meth) acrylate. These can be used alone or in combination of two or more. Among these, tetraethylene glycol mono (meth) acrylate, polyethylene glycol mono (meth) acrylate, tetrapropylene glycol mono (meth) acrylate, and polypropylene glycol mono (meth) acrylate are preferable.

  Specific examples of the (meth) acrylate monomer (A-2) include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, isopropyl (meth) acrylate, (meth) acrylic. N-butyl acid, isobutyl (meth) acrylate, n-amyl (meth) acrylate, isoamyl (meth) acrylate, n-hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, and (meth) Examples include (meth) acrylic acid alkyl esters such as lauryl acrylate. Preferred are methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, and isopropyl (meth) acrylate. These (meth) acrylic acid ester monomers can be used alone or in combination of two or more.

  Specific examples of the (meth) acrylic acid monomer (A-3) include methacrylic acid and acrylic acid, which can be used alone or in combination of two or more. Two combinations of methacrylic acid and acrylic acid may be used in a weight ratio of 1:99 to 99: 1, for example 5:95 to 95: 5, in particular 20:80 to 80:20.

  The polyfunctional (meth) acrylate monomer (B) serves as a crosslinking agent. Examples of the polyfunctional (meth) acrylate monomer (B) include bifunctional to pentafunctional (meth) acrylate. A bifunctional to pentafunctional cross-linking agent is excellent in dispersion by emulsion polymerization and has excellent physical properties (flexibility and binding properties) as a binder. The polyfunctional (meth) acrylate monomer (B) is preferably a trifunctional or tetrafunctional (meth) acrylate.

  Specific examples of the bifunctional (meth) acrylate include triethylene glycol di (meth) acrylate, tetraethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, tripropylene glycol di (meth) acrylate, tetrapropylene glycol di Examples thereof include (meth) acrylate, polypropylene glycol di (meth) acrylate, polytetramethylene glycol di (meth) acrylate, dioxane glycol di (meth) acrylate, and bis (meth) acryloyloxyethyl phosphate.

  Specific examples of trifunctional (meth) acrylates include trimethylolpropane tri (meth) acrylate, trimethylolpropane EO-added tri (meth) acrylate, trimethylolpropane PO-added tri (meth) acrylate, and pentaerythritol tri (meth) acrylate. 2,2,2-tris (meth) acryloyloxymethylethyl succinic acid, ethoxylated isocyanuric acid tri (meth) acrylate, ε-caprolactone modified tris- (2- (meth) acryloxyethyl) isocyanurate, glycerin EO Addition tri (meth) acrylate, glycerin PO addition tri (meth) acrylate, tris (meth) acryloyloxyethyl phosphate, and the like can be mentioned. Among these, trimethylolpropane tri (meth) acrylate, trimethylolpropane EO-added tri (meth) acrylate, and pentaerythritol tri (meth) acrylate are preferable.

  Specific examples of the tetrafunctional (meth) acrylate include ditrimethylolpropane tetra (meth) acrylate, pentaerythritol tetra (meth) acrylate, and pentaerythritol EO-added tetra (meth) acrylate.

  Specific examples of the pentafunctional (meth) acrylate include dipentaerythritol penta (meth) acrylate.

  A polyfunctional (meth) acrylate may be 1 type or can use 2 or more types together.

  The quantity of the structural unit of polyfunctional (meth) acrylate is 0.5-70 weight part with respect to 100 weight part of structural unit (A) of a (meth) acryl monomer, for example, 1-60 weight part, Especially 2-50. It may be part by weight.

  The polymer of the present invention is a polymer containing a structural unit (B) derived from a (meth) acrylic monomer (A) and a polyfunctional (meth) acrylate monomer, and the (meth) acrylic monomer (A) Are derived from a structural unit (A-1) derived from a (meth) acrylate monomer having a hydroxyl group, a structural unit (A-2) derived from a (meth) acrylic acid ester monomer, and a (meth) acrylic acid monomer. The structural unit (A-3) may be included.

  In the polymer, a structural unit derived from a monomer having a hydroxyl group (A-1), a structural unit derived from a (meth) acrylic acid ester monomer (A-2), a structure derived from a (meth) acrylic acid monomer The ratio of the unit (A-3) and the structural unit (B) derived from the polyfunctional (meth) acrylate monomer is (A-1) 1 to 99.9% by weight, (A-2) 69 to 0% by weight. And (A-3) 15 to 0% by weight, (B) 20 to 0.1% by weight, preferably (A-1) 10 to 94% by weight, (A-2) 60 to 5% by weight and ( A-3) 13 to 0% by weight and (B) 18 to 1% by weight.

  Other monomers include fumaric acid, maleic acid, itaconic acid, citraconic acid, mesaconic acid, glutaconic acid, acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, crotonnitrile, α-ethylacrylonitrile, α-cyanoacrylate, vinylidene cyanide Fumaronitrile or the like can be used.

  Examples of the silicone-based and / or mineral oil-based antifoaming agent (C) include dimethylsilicone-based, methylphenylsilicone-based, methylvinylsilicone-based antifoaming agent, and mineral oil-based antifoaming agent, preferably dimethylsilicone-based. Moreover, you may use an antifoamer as an emulsion type antifoamer formed by disperse | distributing in water with surfactant. These antifoaming agents can be used alone or in admixture of two or more.

  The addition amount of the antifoaming agent is 0.001-1 part by weight, preferably 0.005-0.5 part by weight, more preferably 0.005-0.3 part by weight per 100 parts by weight of the polymer. If the amount added exceeds 1 part by weight, the binding properties and battery characteristics may be adversely affected.

  As a method for obtaining the polymer of the present invention, there can be used a general emulsion polymerization method, a soap-free emulsion polymerization method, a seed polymerization method, a method in which a monomer or the like is swollen in seed particles and then polymerized. Specifically, a composition containing a monomer, an emulsifier, a polymerization initiator, water, and a dispersant, a chain transfer agent, a pH adjuster, etc. at room temperature in an airtight container equipped with a stirrer and a heating device is an inert gas. Monomers and the like are emulsified in water by stirring in an atmosphere. As a method of emulsification, a method using stirring, shearing, ultrasonic waves, or the like can be applied, and a stirring blade, a homogenizer, or the like can be used. Next, by starting the polymerization by raising the temperature while stirring, a spherical polymer latex in which the polymer is dispersed in water can be obtained. In addition, the produced spherical polymer may be separately isolated and then dispersed in an organic solvent such as N-methylpyrrolidone using a dispersant or the like. Furthermore, there is a method in which a latex of a polymer is obtained by again dispersing in water using a monomer, an emulsifier, a dispersant, or the like. The monomer addition method at the time of polymerization may be monomer dropping, pre-emulsion dropping, or the like in addition to batch preparation, and two or more of these methods may be used in combination.

  The particle structure of the polymer in the binder of the present invention is not particularly limited. For example, a latex of a polymer containing composite polymer particles having a core-shell structure produced by seed polymerization can be used. As the seed polymerization method, for example, a method described in “Dispersion / Emulsification System Chemistry” (Publisher: Engineering Books Co., Ltd.) can be used. Specifically, this is a method in which a monomer, a polymerization initiator, and an emulsifier are added to a system in which seed particles produced by the above method are dispersed to grow core particles, and the above method may be repeated one or more times.

  You may employ | adopt the particle | grains using the polymer of this invention, or a well-known polymer for seed polymerization. Examples of the known polymer include polyethylene, polypropylene, polyvinyl alcohol, polystyrene, poly (meth) acrylate, and polyether, but are not limited, and other known polymers can be used. Further, one kind of homopolymer or two or more kinds of copolymers or blends may be used.

  In addition to the spherical shape, the particle shape of the polymer in the binder of the present invention includes a plate shape, a hollow structure, a composite structure, a localized structure, a daruma-shaped structure, an octopus-like structure, a raspberry-like structure, and the like. Particles having two or more types of structures and compositions can be used without departing from the scope.

  The emulsifier used in the present invention is not particularly limited, and nonionic emulsifiers, anionic emulsifiers and the like generally used in emulsion polymerization methods can be used. Nonionic emulsifiers include, for example, polyoxyethylene alkyl ether, polyoxyethylene alcohol ether, polyoxyethylene alkyl phenyl ether, polyoxyethylene polycyclic phenyl ether, polyoxyalkylene alkyl ether, sorbitan fatty acid ester, polyoxyethylene fatty acid ester and And polyoxyethylene sorbitan fatty acid esters. Examples of anionic emulsifiers include alkyl benzene sulfonates, alkyl sulfate esters, polyoxyethylene alkyl ether sulfates, fatty acid salts, and the like. You may use above. Representative examples of the anionic emulsifier include sodium dodecylbenzenesulfonate, sodium lauryl sulfate, and triethanolamine lauryl sulfate.

  The amount of the emulsifier used in the present invention may be an amount generally used in the emulsion polymerization method. Specifically, it is in the range of 0.01 to 10% by weight, preferably 0.05 to 5% by weight, more preferably 0.05 to 3% by weight, based on the monomer amount charged.

  The polymerization initiator used by this invention is not specifically limited, The polymerization initiator generally used in an emulsion polymerization method can be used. Specific examples thereof include water-soluble polymerization initiators represented by persulfates such as potassium persulfate, sodium persulfate and ammonium persulfate, and oil-soluble polymerization represented by cumene hydroperoxide and diisopropylbenzene hydroperoxide. Initiator, hydroperoxide, 4-4'-azobis (4-cyanovaleric acid), 2-2'-azobis [2- (2-imidazolin-2-yl) propane, 2-2'-azobis (propane- 2-Carboamidine) 2-2'-azobis [N- (2-carboxyethyl) -2-methylpropanamide, 2-2'-azobis {2- [1- (2-hydroxyethyl) -2-imidazoline- 2-yl] propane}, 2-2′-azobis (1-imino-1-pyrrolidino-2-methylpropane) and 2-2′-azobis {2- And azo initiators such as methyl-N- [1,1-bis (hydroxymethyl) -2-hydroxyethyl] propanamide}, redox initiators, and the like. These polymerization initiators may be used alone or in combination of two or more.

  The amount of the polymerization initiator used in the present invention may be an amount generally used in the emulsion polymerization method. Specifically, it is in the range of 0.01 to 5% by weight, preferably 0.05 to 3% by weight, and more preferably 0.1 to 1% by weight, with respect to the charged monomer amount.

  The water used when producing the binder of the present invention is not particularly limited, and generally used water can be used. Specific examples thereof include tap water, distilled water, ion exchange water, and ultrapure water. Among these, distilled water, ion exchange water, and ultrapure water are preferable.

  In the present invention, a dispersant can be used as necessary, and the kind and amount of use are not particularly limited, and a commonly used dispersant can be freely used in any amount. Specific examples include sodium hexametaphosphate, sodium tripolyphosphate, sodium pyrophosphate and sodium polyacrylate.

  In the present invention, a chain transfer agent can be used as necessary. Specific examples of the chain transfer agent include n-hexyl mercaptan, n-octyl mercaptan, t-octyl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan, n-stearyl mercaptan and other alkyl mercaptans, 2,4-diphenyl-4 -Xanthogen compounds such as methyl-1-pentene, 2,4-diphenyl-4-methyl-2-pentene, dimethylxanthogen disulfide, diisopropylxanthogen disulfide, terpinolene, tetramethylthiuram disulfide, tetraethylthiuram disulfide, tetramethylthiuram Thiuram compounds such as monosulfide, phenol compounds such as 2,6-di-t-butyl-4-methylphenol and styrenated phenol, allyl compounds such as allyl alcohol, Halogenated hydrocarbon compounds such as chloromethane, dibromomethane, carbon tetrabromide, vinyl ethers such as α-benzyloxystyrene, α-benzyloxyacrylonitrile, α-benzyloxyacrylamide, triphenylethane, pentaphenylethane, acrolein, methacrolein , Thioglycolic acid, thiomalic acid, 2-ethylhexyl thioglycolate, and the like, and these may be used alone or in combination. The amount of these chain transfer agents is not particularly limited, but is usually 0 to 5 parts by weight with respect to 100 parts by weight of the charged monomer.

  The polymerization time and polymerization temperature are not particularly limited. Although it can select suitably from the kind etc. of the polymerization initiator to be used, generally polymerization temperature is 20-100 degreeC and superposition | polymerization time is 0.5 to 100 hours.

  Furthermore, the polymer obtained by the above method can be adjusted in pH by using a base as a pH adjuster as necessary. Specific examples of the base include alkali metal (Li, Na, K, Rb, Cs) hydroxide, ammonia, an inorganic ammonium compound, an organic amine compound, and the like. The pH range is pH 1-11, preferably pH 2-11, more preferably pH 2-10, such as pH 3-10, especially pH 5-9.

  The binder of the present invention may generally be a binder composition containing a polymer and water, in particular a binder composition in which the polymer is dispersed in water. The content (solid content concentration) of the polymer in the binder composition of the present invention is 1 to 80% by weight, preferably 5 to 70% by weight, and more preferably 10 to 60% by weight.

  The particle diameter of the polymer in the binder of the present invention can be measured by a dynamic light scattering method, a transmission electron microscope method, an optical microscope method, or the like. The average particle diameter calculated from the scattering intensity obtained using the dynamic light scattering method is 0.001 μm to 1 μm, preferably 0.001 μm to 0.500 μm. Specific examples of the measuring device include Spectris Zetasizer Nano.

Method for adjusting slurry for battery electrode The method for preparing slurry for battery electrode using the binder of the present invention is not particularly limited, and the binder, active material, conductive additive, water, thickener as necessary, etc. of the present invention. May be dispersed using an ordinary stirrer, disperser, kneader, planetary ball mill, homogenizer, or the like. In order to increase the efficiency of dispersion, heating may be performed within a range that does not affect the material.

Production Method of Battery Electrode A production method of the battery electrode is not particularly limited, and a general method is used. For example, a slurry (coating solution) composed of a positive electrode active material or negative electrode active material, a conductive additive, a binder, water, and a thickener as necessary is applied onto the current collector surface by a doctor blade method or a silk screen method. It is performed by uniformly applying to an appropriate thickness.

  For example, in the doctor blade method, a negative electrode active material powder, a positive electrode active material powder, a conductive additive, a binder, and the like are dispersed in water to form a slurry, which is applied to a metal electrode substrate, and then is more appropriate for a blade having a predetermined slit width. Uniform to thickness. The electrode is dried in hot air at 100 ° C. or vacuum at 80 ° C., for example, in order to remove excess water and organic solvent after the active material is applied. An electrode material is manufactured by press-molding the dried electrode with a pressing device. You may heat-process again after pressing, and may remove water, a solvent, an emulsifier, etc.

  The positive electrode material is, for example, a metal electrode substrate as an electrode material substrate, a positive electrode active material on the metal electrode substrate, and a good ion exchange with the electrolyte layer, and the conductive auxiliary agent and the positive electrode active material are fixed to the metal substrate. It is made up of a binder. For example, aluminum is used for the metal electrode substrate, but is not limited thereto, and may be nickel, stainless steel, gold, platinum, titanium, or the like.

The positive electrode active material used in the present invention is a lithium metal-containing composite oxide powder having any composition of LiMO ₂ , LiM ₂ O ₄ , Li ₂ MO ₃ , and LiMEO ₄ . Here, M in the formula is mainly composed of a transition metal and includes at least one of Co, Mn, Ni, Cr, Fe, and Ti. M is made of a transition metal, but Al, Ga, Ge, Sn, Pb, Sb, Bi, Si, P, B, etc. may be added in addition to the transition metal. E contains at least one of P and Si. The particle diameter of the positive electrode active material is preferably 50 μm or less, more preferably 20 μm or less. These active materials have an electromotive force of 3 V (vs. Li / Li +) or more.

  Specific examples of the positive electrode active material include lithium cobaltate, lithium nickelate, nickel / manganese / lithium cobaltate (ternary system), spinel type lithium manganate, and lithium iron phosphate.

  The negative electrode material is, for example, a metal electrode substrate as an electrode material substrate, a negative electrode active material on the metal electrode substrate, and exchange of good ions with the electrolyte layer, and the conductive auxiliary agent and the negative electrode active material are fixed to the metal substrate It is made up of a binder. In this case, for example, copper is used for the metal electrode substrate, but the metal electrode substrate is not limited to this, and may be nickel, stainless steel, gold, platinum, titanium, or the like.

  The negative electrode active material used in the present invention is a carbon material (natural graphite, artificial graphite, amorphous carbon, etc.) having a structure (porous structure) capable of occluding and releasing lithium ions, or occluding and releasing lithium ions. It is a powder made of a metal such as lithium, aluminum-based compound, tin-based compound, silicon-based compound, and titanium-based compound. The particle diameter is preferably from 10 nm to 100 μm, more preferably from 20 nm to 20 μm. Moreover, you may use as a mixed active material of a metal and a carbon material. It is preferable to use a negative electrode active material having a porosity of about 70%.

  Specific examples of the conductive assistant include conductive carbon black such as graphite, furnace black, acetylene black, and ketjen black, or metal powder. These conductive aids may be used alone or in combination of two or more.

Specific examples of the thickener include carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, and sodium salts, ammonium salts, polyvinyl alcohol, and polyacrylates thereof. These thickeners may be used alone or in combination of two or more.
The following battery manufacturing method is mainly a lithium ion secondary battery manufacturing method.

Manufacturing Method of Battery The manufacturing method of the battery, particularly the secondary battery, is not particularly limited, and includes a positive electrode, a negative electrode, a separator, an electrolytic solution, and a current collector, and is manufactured by a known method. For example, in the case of a coin-type battery, a positive electrode, a separator, and a negative electrode are inserted into an outer can. This is impregnated with an electrolytic solution. Then, it joins with a sealing body by tab welding etc., a sealing body is enclosed, and a storage battery is obtained by crimping. The shape of the battery is not limited, but examples include a coin type, a cylindrical type, and a sheet type, and a structure in which two or more batteries are stacked may be used.

  As the separator, a positive electrode and a negative electrode are directly contacted to prevent short-circuiting in the storage battery, and a known material can be used. Specifically, it is made of a porous polymer film such as polyolefin or paper. As the porous polymer film, a film such as polyethylene or polypropylene is preferable because it is not affected by the electrolytic solution.

The electrolytic solution is a solution comprising an electrolyte lithium salt compound and an aprotic organic solvent as a solvent. As the electrolyte lithium salt compound, a lithium salt compound having a wide potential window, which is generally used in lithium ion batteries, is used. For example, LiBF ₄ , LiPF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN [CF ₃ SC (C ₂ F ₅ SO ₂ ) ₃ ] _{2 and the} like, but are not limited thereto. These may be used alone or in combination of two or more.

  As aprotic organic solvents, propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, γ-butyrolactone, tetrahydrofuran, 1,3-dioxolane, Linear ethers such as dipropyl carbonate, diethyl ether, sulfolane, methyl sulfolane, acetonitrile, propyl nitrile, anisole, acetic acid ester, propionic acid ester, diethyl ether can be used. Good.

  Moreover, room temperature molten salt can be used as a solvent. The room temperature molten salt refers to a salt that is at least partially in a liquid state at room temperature, and the room temperature refers to a temperature range in which a power supply is assumed to normally operate. The temperature range in which the power supply is assumed to normally operate has an upper limit of about 120 ° C. and in some cases about 60 ° C., and a lower limit of about −40 ° C. and in some cases about −20 ° C.

  The room temperature molten salt is also called an ionic liquid and is a “salt” composed of only ions (anions and cations), and in particular, a liquid compound is called an ionic liquid.

  Known cationic species include pyridine, aliphatic amine, and alicyclic amine quaternary ammonium organic cations. Examples of the quaternary ammonium organic cation include imidazolium ions such as dialkylimidazolium and trialkylimidazolium, tetraalkylammonium ions, alkylpyridinium ions, pyrazolium ions, pyrrolidinium ions, and piperidinium ions. In particular, an imidazolium cation is preferable.

  Examples of tetraalkylammonium ions include, but are not limited to, trimethylethylammonium ion, trimethylethylammonium ion, trimethylpropylammonium ion, trimethylhexylammonium ion, tetrapentylammonium ion, and triethylmethylammonium ion. is not.

  Examples of the alkyl pyridinium ion include N-methyl pyridinium ion, N-ethyl pyridinium ion, N-propyl pyridinium ion, N-butyl pyridinium ion, 1-ethyl-2methyl pyridinium ion, 1-butyl-4-methyl. Examples thereof include, but are not limited to, pyridinium ions and 1-butyl-2,4 dimethylpyridinium ions.

  Examples of the imidazolium cation include 1,3-dimethylimidazolium ion, 1-ethyl-3-methylimidazolium ion, 1-methyl-3-ethylimidazolium ion, 1-methyl-3-butylimidazolium ion, 1- Butyl-3-methylimidazolium ion, 1,2,3-trimethylimidazolium ion, 1,2-dimethyl-3-ethylimidazolium ion, 1,2-dimethyl-3-propylimidazolium ion, 1-butyl- Examples include 2,3-dimethylimidazolium ion, but are not limited thereto.

Examples of the anionic species include halide ions such as chloride ions, bromide ions, and iodide ions, perchlorate ions, thiocyanate ions, tetrafluoroborate ions, nitrate ions, inorganic acids such as AsF ₆ ⁻ and PF ₆ ^−. Organic acid ions such as ions, stearyl sulfonate ions, octyl sulfonate ions, dodecylbenzene sulfonate ions, naphthalene sulfonate ions, dodecyl naphthalene sulfonate ions, 7,7,8,8-tetracyano-p-quinodimethane ions Etc. are exemplified.

  In addition, normal temperature molten salt may be used independently, or may mix and use 2 or more types.

Various additives can be used in the electrolytic solution as necessary. For example, brominated epoxy compounds, phosphazene compounds, tetrabromobisphenol A as flame retardants and flame retardants
And halides such as chlorinated paraffin, antimony trioxide, antimony pentoxide, aluminum hydroxide, magnesium hydroxide, phosphate ester, polyphosphate, and zinc borate. Examples of the negative electrode surface treatment agent include vinylene carbonate, fluoroethylene carbonate, and polyethylene glycol dimethyl ether. Examples of the positive electrode surface treatment agent include inorganic compounds such as carbon and metal oxides (such as MgO and ZrO ₂ ), and organic compounds such as ortho-terphenyl. Examples of the overcharge inhibitor include biphenyl and 1- (p-tolyl) adamantane.

  Specific modes for carrying out the present invention will be described below with reference to examples. However, the present invention is not limited to the following examples without departing from the gist thereof.

  In this example, using the binder composition of the present invention, a foaming test is performed to produce an electrode and a coin battery, and a flex test, an adhesion test, and a charge / discharge cycle characteristic performance as an evaluation of a coin battery are as follows. The experiment was conducted.

[Bubbling test of binder composition]
In the foaming test, after synthesizing the binder latex in a 30 ml graduated cylinder, immediately put 5 ml of the binder composition to which the antifoaming agent was added, blow in nitrogen (50 ml / min) for 30 seconds, and the volume of the foam after standing for 3 minutes. Was measured. Furthermore, in order to investigate the sustainability as an antifoaming agent, after standing for 1 week, nitrogen (50 ml / min) was blown again for 30 seconds, and the volume of the foam after standing for 3 minutes was measured. The evaluation results are summarized in Table 1.

[Evaluation of fabricated electrode]
As evaluation of the produced electrode, a bending test and an adhesion test were performed. The evaluation results are summarized in Table 2.
Bending test The bending test was performed by a mandrel bending test. Specifically, the electrode is cut into a width of 3 cm and a length of 8 cm, and 180 ° with a stainless steel rod having a diameter of 2 mm on the base side (the electrode surface faces the outside) at the center (4 cm portion) in the length direction. The state of the coating film at the bent portion when bent was observed. Measurement is performed 5 times by this method, and the case where the electrode surface is not cracked or peeled off or peeled off from the current collector at all 5 times. The case where one or more cracks or peeling occurs even once. It was evaluated.

Adhesion test (binding test)
The adhesion test was performed by a cross cut test. Specifically, the electrode is cut to a width of 3 cm × length of 4 cm, and a grid pattern is cut with a cutter knife so that one side of one square is 1 mm, and from 25 squares of vertical 5 squares × horizontal 5 squares. When a tape (cello tape (registered trademark): manufactured by Nichiban) was applied to the grid, and the tape was peeled off at a stretch with the electrode fixed, the number of cells remaining without being peeled off from the electrode was measured. The test was performed 5 times, and the average value was obtained.

[Evaluation of fabricated battery]
As evaluation of the produced battery, a charge / discharge cycle characteristic test was performed using a charge / discharge device, and a capacity retention rate was obtained. The evaluation results are summarized in Table 1.
Capacity maintenance rate The electrochemical characteristics were measured using a charge / discharge device manufactured by Nagano Co., Ltd., with 4.2 V upper limit and 2.5 V as the lower limit. C / 8) The charging / discharging cycle characteristics of the battery were evaluated by conducting a constant current under test conditions (C / 4) in which predetermined charging and discharging can be performed in 4 hours after the fourth time. The test temperature was 60 ° C. The value of the discharge capacity at the 4th cycle was adopted as the reversible capacity, and the capacity maintenance rate was evaluated by the ratio of the discharge capacity after 100 cycles of charge / discharge and the discharge capacity at the 4th cycle.

Example of synthesis of binder composition (Example 1)
[Exemplary Synthesis Example 1 of Binder Composition]
In a reaction vessel equipped with a stirrer, 45 parts by weight of methyl methacrylate, 45 parts by weight of polypropylene glycol monoacrylate (manufactured by NOF: Blemmer AP-400, molecular weight 420), 1.3 parts by weight of acrylic acid, 3.7 parts by weight of methacrylic acid, 5 parts by weight of trimethylolpropane triacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd .: A-TMPT), 1 part by weight of sodium lauryl sulfate as an emulsifier, 500 parts by weight of ion-exchanged water and 1 part by weight of potassium persulfate as a polymerization initiator The mixture was sufficiently emulsified using a homogenizer, heated to 60 ° C. under a nitrogen atmosphere, polymerized for 5 hours, and then cooled. After cooling, the pH of the polymerization solution was adjusted to 6.5 using a 24% aqueous sodium hydroxide solution to obtain a binder (latex) (polymerization conversion rate 99% or more, solid content concentration 17 wt%). The average particle diameter of the obtained polymer was 0.097 μm.
0.28 parts by weight of a mineral oil-based antifoaming agent (manufactured by SN Deformer 777 San Nopco) was added to 100 parts by weight of the polymer to obtain a binder composition A. The evaluation results of the foaming test are shown in Table 1.

(Example 2)
[Exemplary Synthesis Example 2 of Binder Composition]
Example of binder composition In place of the antifoaming agent of Synthesis Example 1, 0.28 parts by weight of a mineral oil-based antifoaming agent (manufactured by SN Deformer 154S San Nopco) is added to 100 parts by weight of the polymer, and the binder composition B It was. The evaluation results of the foaming test are shown in Table 1.

(Example 3)
[Exemplary Synthesis Example 3 of Binder Composition]
Example of Binder Composition Instead of the antifoaming agent of Synthesis Example 1, a dimethyl silicone antifoaming agent (manufactured by YMA 6509 Momentive Co., Ltd.) was added in an amount of 0.000056 part by weight based on 100 parts by weight of the polymer. did. The evaluation results of the foaming test are shown in Table 1.

Example 4
[Exemplary Synthesis Example 4 of Binder Composition]
Example of binder composition Instead of the antifoaming agent of Synthesis Example 1, dimethylsilicone antifoaming agent (TSA7341 Momentive Co., Ltd.) was added in an amount of 0.000056 part by weight with respect to 100 parts by weight of the polymer. did. The evaluation results of the foaming test are shown in Table 1.

(Comparative Example 1)
[Comparative Synthesis Example 1 of Binder Composition]
Example of binder composition The binder composition E was prepared without adding the antifoaming agent of Synthesis Example 1. The evaluation results of the foaming test are shown in Table 1.

(Comparative Example 2)
[Comparative Synthesis Example 2 of Binder Composition]
Example of binder composition Instead of the antifoaming agent of Synthesis Example 1, a polyether antifoaming agent (manufactured by SN Deformer 470 San Nopco) was added in an amount of 0.28 parts by weight based on 100 parts by weight of the polymer. F. The evaluation results of the foaming test are shown in Table 1.

(Comparative Example 3)
[Comparative Synthesis Example 3 of Binder Composition]
Example of Binder Composition Instead of the antifoaming agent in Synthesis Example 1, 0.28 parts by weight of a polyether antifoaming agent (manufactured by SN Deformer 260 San Nopco) is added to 100 parts by weight of the polymer, and the binder composition is added. G. The evaluation results of the foaming test are shown in Table 1.

(Comparative Example 4)
[Comparative Synthesis Example 4 of Binder Composition]
In a reaction vessel equipped with a stirrer, 48 parts by weight of methyl methacrylate, 40 parts by weight of polypropylene glycol monoacrylate (manufactured by NOF: Blemmer AP-400), 4 parts by weight of acrylic acid, 8 parts by weight of methacrylic acid, dodecylbenzenesulfone as an emulsifier 1 part by weight of sodium acid, 500 parts by weight of ion-exchanged water and 1 part by weight of potassium persulfate as a polymerization initiator were added and sufficiently emulsified using an ultrasonic homogenizer, and then heated to 60 ° C. in a nitrogen atmosphere. The polymer did not become fine particles but settled in about 1 hour when stirred. While stirring, the pH was adjusted to 6.9 using an aqueous sodium hydroxide solution to obtain a binder composition H. (Because it was not latex, no antifoam was added.

本発明のバインダー組成物は泡立ち試験より、比較例と対比して、優れていることが明らかである。 Table 1 shows the evaluation results of the foaming test.

From the foam test, it is clear that the binder composition of the present invention is superior to the comparative example.

Example of electrode preparation
[Example 1 of positive electrode production]
90.6 parts by weight of nickel / manganese / lithium cobaltate (ternary system) as a positive electrode active material, 6.4 parts by weight of acetylene black as a conductive assistant, binder composition obtained in Example Synthesis Example 3 of binder composition Add 1 part by weight as the solid content of C and 2 parts by weight of sodium salt of carboxymethyl cellulose as the thickener, and further add water as a solvent so that the solid content concentration of the slurry is 35% by weight, and use a planetary mill. Thorough mixing was performed to obtain a positive electrode slurry.
The obtained positive electrode slurry was coated on a 20 μm thick aluminum current collector using a 150 μm gap blade coater, dried at 110 ° C. in a vacuum state for 12 hours or more, and then pressed with a roll press machine. A 34 μm positive electrode was produced. The evaluation results of flexibility and binding properties are shown in Example 5 in Table 2.

[Example 2 of positive electrode production]
Example of binder composition A positive electrode having a thickness of 34 µm was produced in the same manner as in Example 1 of producing a positive electrode except that the binder composition D obtained in Synthesis Example 4 was used. Evaluation results of flexibility and binding property are shown in Example 6 of Table 2.

[Comparative Example 1 of Positive Electrode]
A positive electrode was produced in the same manner as in Example 1 of producing an electrode except that the binder composition H obtained in Comparative Synthesis Example 4 of the binder composition was used. The thickness of the positive electrode obtained was 36 μm. The evaluation results of the flexibility and binding property are shown in Comparative Example 5 in Table 2.

[Comparative Example 2 of Positive Electrode]
88.7 parts by weight of nickel / manganese / lithium cobaltate (ternary system) as the positive electrode active material, 6.3 parts by weight of acetylene black as the conductive auxiliary agent, and polyvinylidene fluoride (PVDF, solid content concentration of 12 wt% N as the binder) -Methyl-2-pyrrolidone solution) 5.0 parts by weight is added, and N-methyl-2-pyrrolidone is added as a solvent so that the solid content concentration of the slurry is 40%, and the mixture is thoroughly mixed using a planetary mill. Thus, a slurry solution for the positive electrode was obtained.
A positive electrode was produced in the same manner as in Example 1 for producing electrodes except that the slurry solution thus obtained was used. The thickness of the obtained positive electrode was 35 μm. The evaluation results of the flexibility and binding property are shown in Comparative Example 6 in Table 2.

[Example 1 of production of negative electrode]
95 parts by weight of artificial graphite as a negative electrode active material, 2 parts by weight of vapor grown carbon fiber (VGCF) as a conductive additive, and 1 part by weight of binder composition C obtained in Example Synthesis Example 3 of the binder composition as a solid content Add 2 parts by weight of sodium carboxymethylcellulose as a thickener, add water as a solvent so that the solid content concentration of the slurry is 35% by weight, and mix well using a planetary mill. A slurry was obtained.
The obtained negative electrode slurry was applied onto a 20 μm thick copper current collector using a 130 μm gap blade coater, dried at 110 ° C. in a vacuum state for 12 hours or more, and then pressed with a roll press to obtain a thickness. A 28 μm negative electrode was produced. The evaluation results of flexibility and binding properties are shown in Example 7 in Table 2.

[Example 2 of negative electrode production]
Example of Binder Composition A negative electrode having a thickness of 31 μm was produced in the same manner as in Example 1 of producing a negative electrode except that the binder composition D obtained in Synthesis Example 4 was used. The evaluation results of the flexibility and binding property are shown in Example 8 in Table 2.

[Comparative Example 1 of Negative Electrode]
A negative electrode was produced in the same manner as in Example 1 for producing a negative electrode except that the binder composition H obtained in Comparative Synthesis Example 4 of the binder composition was used. The thickness of the obtained negative electrode was 36 μm. The evaluation results of flexibility and binding properties are shown in Comparative Example 7 in Table 2.

[Comparative Example 2 of Negative Electrode]
95 parts by weight of artificial graphite as a negative electrode active material, 2 parts by weight of vapor grown carbon fiber (VGCF) as a conductive additive, and polyvinylidene fluoride as a binder (PVDF, N-methyl-2-pyrrolidone solution with a solid content concentration of 12 wt%) 3 parts by weight was added, and N-methyl-2-pyrrolidone was added as a solvent so that the solid content concentration of the slurry was 35% by weight, followed by thorough mixing using a planetary mill to obtain a negative electrode slurry.
The obtained negative electrode slurry was applied onto a 20 μm thick copper current collector using a 130 μm gap blade coater, dried at 110 ° C. in a vacuum state for 12 hours or more, and then pressed with a roll press to obtain a thickness. A 29 μm negative electrode was produced. The evaluation results of flexibility and binding property are shown in Comparative Example 8 in Table 2.

Coin battery manufacturing
[Example of battery production 1]
In the glove box substituted with argon gas, the positive electrode obtained in Example 1 of the positive electrode, two polypropylene / polyethylene / polypropylene porous membranes having a thickness of 18 μm as separators, and a metal lithium foil having a thickness of 300 μm as a counter electrode. A 2032 type coin battery for testing is obtained by sufficiently impregnating the laminated product with 1 mol / L lithium hexafluorophosphate ethylene carbonate and dimethyl carbonate solution (volume ratio 1: 1) as an electrolytic solution. Manufactured. The evaluation results of the capacity retention rate after 100 cycles are shown in Example 5 of Table 2.

[Example of battery production 2]
A coin battery was produced in the same manner as in the battery production example 1 except that the positive electrode obtained in the positive electrode production example 2 was used. The evaluation results of the capacity retention rate after 100 cycles are shown in Example 6 of Table 2.

[Example 3 of battery production]
A coin battery was produced in the same manner as in the battery production example 1 except that the negative electrode obtained in the negative electrode production example 1 was used instead of the positive electrode. The evaluation results of the capacity retention rate after 100 cycles are shown in Example 7 in Table 2.

[Example 4 of battery production]
A coin battery was produced in the same manner as in the battery production example 1 except that the negative electrode obtained in the negative production example 2 was used instead of the positive electrode. The evaluation results of the capacity retention rate after 100 cycles are shown in Example 8 in Table 2.

[Battery Comparative Production Example 1]
A coin battery was produced in the same manner as in the battery production example 1 except that the positive electrode obtained in Comparative production example 1 of the positive electrode was used. The evaluation results of the capacity retention rate after 100 cycles are shown in Comparative Example 5 in Table 2.

[Battery Comparative Production Example 2]
A coin battery was produced in the same manner as in the battery production example 1 except that the positive electrode obtained in Comparative production example 2 of the positive electrode was used. The evaluation result of the capacity retention rate after 100 cycles is shown in Comparative Example 6 in Table 2.

[Battery Comparative Production Example 3]
A coin battery was produced in the same manner as in Example 1 of the battery except that the negative electrode obtained in Comparative Production Example 1 of the negative electrode was used instead of the positive electrode. The evaluation results of the capacity retention rate after 100 cycles are shown in Comparative Example 7 in Table 2.

[Battery Comparative Production Example 4]
A coin battery was produced in the same manner as in Example 1 of the battery except that the negative electrode obtained in Comparative Production Example 2 of the negative electrode was used instead of the positive electrode. The evaluation results of the capacity retention rate after 100 cycles are shown in Comparative Example 8 in Table 2.

Table 2 shows the evaluation results in Examples and Comparative Examples.

  The binder composition for a battery electrode of the present invention has good dispersibility of each component during electrode slurry preparation, improves the slurry coating property, and can suppress bubbles remaining in the electrode. Moreover, it has the advantage that it is a water system with high binding force and a small environmental load, and the performance does not affect the temperature. Secondary batteries using this binder, especially lithium ion secondary batteries, can be used for small-sized batteries such as mobile phones, laptop computers, camcorders and other electronic devices, for in-vehicle applications such as electric vehicles and hybrid electric vehicles, and for household power storage. It can be suitably used for large-sized secondary battery applications such as storage batteries.

Claims (8)

A polymer comprising (A) a (meth) acrylic monomer and (B) a structural unit derived from a polyfunctional (meth) acrylate monomer;
(C) A binder composition for battery electrodes, comprising a silicone-based and / or mineral oil-based antifoaming agent.   The binder composition for battery electrodes according to claim 1, wherein the (meth) acrylic monomer (A) is a (meth) acrylate monomer having a hydroxyl group.   The battery electrode binder composition according to claim 2, wherein the (meth) acrylate monomer having a hydroxyl group is an alkylene glycol mono (meth) acrylate having a molecular weight of 100 to 1,000.   The binder composition for battery electrodes according to any one of claims 1 to 3, wherein the polyfunctional (meth) acrylate (B) is a 3-5 functional (meth) acrylate.   The binder composition for battery electrodes according to any one of claims 1 to 4, wherein the silicone-based antifoaming agent is a dimethyl silicone-based.   The battery electrode binder composition according to any one of claims 1 to 5, wherein the battery is a secondary battery.   A battery electrode comprising the binder composition according to claim 1 and an active material.   A battery comprising the electrode according to claim 7.