JP2000058061A - Nickel-hydrogen battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nickel-hydrogen battery superior in durability at high temperature with little reduction in battery capacity accompanying the progress of charging/discharging cycles. SOLUTION: In a nickel-hydrogen battery having a positive electrode and a negative electrode, each having a layer including a polymer binder and an active material, as the polymer binder included in at least one of the positive electrode and negative electrode, preferably in both of them, a (meth)acrylic ester copolymer is used having 30 wt.% or more of repeated structural units derived from a (meth)acrylic alkyl ester having 6c or higher alkyl groups bonded to non-carbonyl oxygen atoms of ester bond and 5 wt.% or more of repeated structural units derived from an aromatic vinyl compound.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nickel-metal hydride battery, and more particularly to a nickel-metal hydride battery having excellent durability at high temperature use and having a small capacity decrease with the progress of charge / discharge cycles.

[0002]

2. Description of the Related Art A nickel-metal hydride battery has a structure in which an electrode group formed between a positive electrode and a negative electrode via a separator is housed in a container together with an alkaline electrolyte. The positive electrode is made by binding additives such as nickel hydroxide and nickel oxyhydroxide, which are active materials, and carbon and cobalt powders, which are conductive materials, to each other with a binder and then to a metal current collector. It is. For the negative electrode, a conductive material such as nickel powder or carbon and a binder are added to a hydrogen storage alloy and kneaded in the presence of water, and the prepared paste is punched metal, a metal perforated plate, a foamed metal plate, and a sintered metal fiber sintered material. Apply to a metal current collector such as a plate,
By drying, the hydrogen storage alloy and the conductive material are bound to each other and further bound to the metal current collector. Therefore, it is necessary that the binder has a high binding force between the current collector and the active material and between the conductive materials and between the materials, and maintains a state in which the active material is bound even after performing a charge / discharge cycle. Therefore, it is necessary to prevent the active material from dropping from the electrode to reduce the battery capacity.

Usually, styrene-butadiene copolymer, acrylic polymer,
Non-water-soluble polymers such as fluoropolymers such as polytetrafluoroethylene (PTFE), ethylene-propylene-diene copolymer rubber (EPDM), and styrene-ethylene-butene-styrene (SEBS) block copolymer rubber And a mixture with a water-soluble polymer such as polyvinyl alcohol, a polyacrylate, a water-soluble cellulose derivative, polyethylene oxide, or polyvinylpyrrolidone, if necessary (Japanese Patent Laid-Open No. 3-28).
No. 3362, JP-A-4-121958, JP-A-4-206345, JP-A-4-272656, JP-A-6-140033, JP-A-8-29
8120, JP-A-9-63589, etc.).

Conventionally, alkali-resistant polymers such as polyvinyl alcohol, fluororesin, and styrene-butadiene rubber have been used as binders. However, there are problems such as a decrease in charge / discharge cycle life and a decrease in battery capacity. In order to solve these problems, research on a binder material has been conducted. For example, ethylene-
Use of a binder composed of a vinyl acetate-long-chain vinyl ester copolymer (JP-A-9-161803) and use of a copolymer of acrylic acid or acrylate and vinyl alcohol (JP-A-7-226205)
Publication). For the positive electrode, use is made of a copolymer of a monomer containing a carboxylic acid or a metal salt of a carboxylic acid and vinyl alcohol (JP-A-8-3398).
No. 07 publication) and the like.

However, with such a binder, the binding force of the active material to the current collector is still insufficient. As the charge / discharge cycle progresses, the active material gradually drops from the current collector, and There was a problem that performance deteriorated. In particular, there has been a problem that the temperature is repeatedly increased to 70 ° C. or higher due to heat generation during charging and discharging, or the capacity is rapidly reduced when exposed to a high temperature environment of 50 ° C. or higher for a long time.

[0006]

Based on such prior art, the present inventors have studied to obtain a binder for a nickel-metal hydride battery having excellent durability at high temperatures and excellent charge / discharge characteristics. (Meth) acrylic ester based copolymer comprising 30% by weight or more of alkyl acrylate units having 6 or more carbon atoms in the alkyl group bonded to the non-carbonyl oxygen atom of the bond and 5% by weight or more of aromatic vinyl compound units When an electrode is made using a binder containing a coalesced substance (hereinafter sometimes simply referred to as a “(meth) acrylate-based copolymer”), it is excellent in durability at high temperatures and has excellent properties such as an active material and a conductive material. Of the present invention by strongly binding the additive of the present invention to the current collector and further reducing the battery capacity as the charge / discharge cycle progresses. And it has completed.

[0007]

Thus, according to the present invention, there is provided a nickel-metal hydride battery using a hydrogen storage alloy as a negative electrode active material and nickel hydroxide or nickel oxyhydroxide as a positive electrode active material, respectively. At least one of the repeating structural units 30 derived from an alkyl acrylate having an alkyl group bonded to a non-carbonyl oxygen atom of an ester bond having 6 or more carbon atoms;
A nickel-metal hydride battery having a layer containing a (meth) acrylate copolymer having at least 5% by weight and at least 5% by weight of a repeating structural unit derived from an aromatic vinyl compound, and an active material is provided. .

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a nickel-metal hydride battery of the present invention will be described in detail. The nickel-metal hydride battery according to the present invention is characterized in that at least one, and preferably both, of the negative electrode having a hydrogen storage alloy as an active material and the positive electrode having nickel hydroxide or nickel oxyhydroxide as the active material have the above-mentioned (meth) acrylate. It has a layer containing a system copolymer as a binder.

1) Negative electrode 1-1) Binder The monomer used in the production of the (meth) acrylate copolymer used in the present invention has a carbon number of an alkyl group bonded to a non-carbonyl oxygen atom of an ester bond. Alkyl acrylates and / or methacrylates having 6 or more; and aromatic vinyl compounds.

Specific examples of alkyl (meth) acrylates having 6 or more carbon atoms in the alkyl group bonded to the non-carbonyl oxygen atom of the ester bond include n-hexyl acrylate, 2-ethylhexyl acrylate, and acrylic acid. Alkyl acrylate monomers such as isooctyl acrylate, isodecyl acrylate, lauryl acrylate, stearyl acrylate, and tridecyl acrylate; and 2-ethylhexyl methacrylate, isooctyl methacrylate, isodecyl methacrylate, lauryl methacrylate, and methacrylic acid An alkyl group bonded to a non-carbonyl oxygen atom of an ester bond such as tridodecyl or stearyl methacrylate has 6 to 20 carbon atoms. Of these, alkyl methacrylate monomers having 8 to 18 carbon atoms are particularly preferred. Specific examples of the aromatic vinyl compound include styrene, α-methylstyrene, β-methylstyrene, pt-butylstyrene, vinylnaphthalene, and a macromonomer in which methacrylate is introduced into a polystyrene terminal. Is preferred.

[0011] The lower limit of the amount of the alkyl (meth) acrylate used is 30 parts by weight or more, preferably 45 parts by weight, based on 100 parts by weight in total with the aromatic vinyl compound.
It is at least 60 parts by weight, more preferably at least 60 parts by weight. The upper limit is not particularly limited, but is usually 95 parts by weight or less, preferably 90 parts by weight or less. If the amount is less than 30 parts by weight, the retention of binding decreases, while if it is too large, the durability at high temperatures decreases. The lower limit of the amount of the aromatic vinyl compound used is 5 parts by weight or more, preferably 10 parts by weight or more, more preferably 15 parts by weight or more, based on 100 parts by weight in total with the alkyl (meth) acrylate. . The upper limit is not particularly limited, but is usually 70 parts by weight or less, preferably 60 parts by weight or less, more preferably 50 parts by weight or less. If the amount is less than 5 parts by weight, the durability at high temperature is reduced, and if it is too large, the binding retention is reduced.

In preparing the (meth) acrylate copolymer used in the present invention, other ethylenically unsaturated monomers may be copolymerized in addition to the alkyl (meth) acrylate and the aromatic vinyl compound, if desired. It is also possible to polymerize. However, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate,
Isopropyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, (meth)
Alkyl (meth) acrylates having an alkyl group with less than 6 carbon atoms, such as n-amyl acrylate and isoamyl (meth) acrylate, have low durability to high temperatures when copolymerized in large amounts. It is usually at most 20% by weight, preferably at most 10% by weight, more preferably at most 5% by weight, based on the total monomer weight. Also,
When a large amount of ionic monomers, such as unsaturated monocarboxylic acid monomers such as acrylic acid and methacrylic acid, are copolymerized, the copolymer gradually reacts with the electrolytic solution to achieve binder performance. The amount used is usually 5% by weight or less based on the total monomer weight,
It is preferably at most 3% by weight, more preferably at most 1% by weight. Other specific examples of the copolymerizable ethylenically unsaturated monomer include non-alkyl hydrocarbon groups such as cyclohexyl (meth) acrylate, isobornyl (meth) acrylate, benzyl (meth) acrylate, and dicyclopentenyl (meth) acrylate. (Meth) acrylic acid ester having methoxyethyl (meth) acrylate, butoxyethyl (meth) acrylate, phenoxyethyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 2 -Hydroxybutyl (meth) acrylate, glycidyl (meth) acrylate, tetrahydrofurfuryl (meth) acrylate, polyoxyethylene glycol mono (meth) acrylate and polyoxypropylene glycol An oxygen-containing hydrocarbon group such as glycol monomethyl (meth) acrylate (meth)
Acrylic esters are mentioned, but the amount of these is preferably less than 40% by weight based on the total monomer weight.

The above (meth) acrylate copolymer can be obtained by a polymerization method such as emulsion polymerization, suspension polymerization and dispersion polymerization. Preferably, an emulsion polymerization method is employed, and among emulsion polymerization, multi-stage polymerization such as seed polymerization is particularly preferred. In the emulsion polymerization, the method of adding the monomer may be any method such as batch addition, continuous addition, and divisional addition. The form of the monomer to be added may be an emulsion prop or only the monomer. Further, a hydrophilic organic solvent such as alcohol or ketone may be added to the polymerization system as needed.

In preparing the (meth) acrylic ester copolymer by emulsion polymerization, a surfactant used in the synthesis of a polymer by a usual emulsion polymerization method can be used. Specifically, examples of the anionic surfactant include benzenesulfonates such as sodium dodecylbenzenesulfonate and sodium dodecylphenylethersulfonate; alkyl sulfates such as sodium lauryl sulfate and sodium tetradodecyl sulfate; sodium dioctyl sulfosuccinate Sulfosuccinates such as sodium dihexylsulfosuccinate; fatty acid salts such as sodium laurate; ethoxysulfate salts such as sodium polyoxyethylene lauryl ether sulfate and sodium polyoxyethylene nonylphenyl ether tersulfate; alkane sulfonates; Alkyl ether phosphate sodium salt and the like.

Examples of the nonionic surfactant include polyoxyethylene lauryl ether, polyoxyethylene cetyl ether, polyoxyethylene stearyl ether,
Polyoxyethylene alkyl ethers such as polyoxyethylene oleyl ether; polyoxyethylene alkyl aryl ethers such as polyoxyethylene nonyl phenyl ether and polyoxyethylene octyl phenyl ether; polyethylene glycol fatty acid esters; polyethylene glycol phosphate esters; sorbitan fatty acid esters; Monoglyceride; polyglycerin fatty acid ester; propylene glycol fatty acid ester; sucrose fatty acid ester; polyoxyethylene-polyoxypropylene block copolymer; polyoxyethylene-polyoxypropylene alkyl ether; ethylene oxide derivative of alkylphenol formalin condensate; polyoxyethylene Glycerin fatty acid ester; polyoxyethylene hydrogenated castor oil; It can be mentioned nonionic surfactants such as polyoxyethylene fatty acid amides; polyoxyethylene sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters; fatty acid alkanolamides.

Preferably, sodium dodecylbenzenesulfonate, sodium lauryl sulfate and polyoxyethylene alkylaryl ether are used. These surfactants may be used alone or in combination of two or more. The amount of the surfactant used in the emulsion polymerization can be arbitrarily set, and is usually about 0.01 to 20 parts by weight based on 100 parts by weight of the total amount of the monomers. Regarding the method of adding the surfactant, the whole amount may be added at once, or may be added continuously or intermittently.

The polymerization initiator used in the emulsion polymerization is not particularly limited, and specific examples thereof include persulfates such as sodium persulfate, potassium persulfate, and ammonium persulfate; hydrogen peroxide; Ketone peroxides such as methyl ethyl ketone peroxide, methyl isobutyl ketone peroxide, cyclohexanone peroxide, methylcyclohexanone peroxide, 3,5,5-trimethylcyclohexanone peroxide;
t-butyl peroxide, t-butyl-α-cumyl peroxide, dicumyl peroxide, 1,3-bis (t-
Butylperoxyisopropyl) benzene, 1,4-bis (t-butylperoxyisopropyl) benzene,
Dialkyl peroxides such as 2,5-dimethyl-2,5-di (t-butylperoxy) hexane and 2,5-dimethyl-2,5-di (t-butylperoxy) hexyne; acetyl peroxide, propionyl Peroxide, isobutyryl peroxide, octanoyl peroxide, 3,5,5-trimethylhexanoyl peroxide, decanoyl peroxide, lauroyl peroxide, benzoyl peroxide, p-chlorobenzoyl peroxide, 2,4-dichloro Diacyl peroxides such as benzoyl peroxide and acetylcyclohexanesulfonyl peroxide; t-butyl hydroperoxide, cumene hydroperoxide, diisopropylbenzene hydroperoxide, p-menthane hydroperoxide, 2,5-dimethyl San-2,5-dihydro peroxide, hydroperoxides such as 1,1,3,3-tetramethylbutyl hydroperoxide; di-2
Ethylhexyl peroxydicarbonate, diisopropylperoxydicarbonate, di-sec-butylperoxydicarbonate, di-n-propylperoxydicarbonate, dimethoxyisopropylperoxydicarbonate, di-3-methoxybutylperoxydicarbonate, Peroxydicarbonates such as di-2-ethoxyethylperoxydicarbonate, bis (4-t-butylcyclohexyl) peroxydicarbonate, t-butylperoxyisopropylcarbonate;
1,1-bis-t-butylperoxy-3,3,5-trimethylcyclohexane, n-butyl-4,4-bis (t-butylperoxy) valerate, 2,2-bis (t-butylperoxy) ) Peroxyketals such as butane; t-butyl peroxyacetate, t-butyl peroxyisobutyrate, t-butyl peroxyoctoate, t-butyl peroxydecanoate, di-t-
Butyl peroxyphthalate, di-t-butyl peroxyisophthalate, t-butyl peroxy laurate,
Organic peroxides such as alkyl peresters such as 2,5-dimethyl-2,5-dibenzoylperoxyhexane; 2,2′-azobisisobutyronitrile, 2,2 ′
Azobis (2,4-dimethylvaleronitrile), 2,
2′-azobis (4-methoxy-2,4-dimethylvaleronitrile), 2,2′-azobis (2- (hydroxymethyl) propionitrile), 1,1-azobis (cyclohexane-1-carbonitrile), 2- (carbomileazo) isobutyronitrile, 2-phenylazo-4-
Methoxy-2,4-dimethylvaleronitrile, 2,2 ′
-Azonitrile compounds such as -azobis (2-methylbutyronitrile); 2,2'-azobis (2-methylpropionamide) dihydrate, 2,2'-azobis (2-methyl-N- (1,1 -Bis (hydroxymethyl) ethyl)
Azoamide compounds such as propionamide) and 2,2'-azobis (2-methyl-N- (1,1-bis (hydroxymethyl) -2-hydroxyethyl) propionamide); 2,2'-azobis (2- Methylpropane),
Alkyl azo compounds such as 2,2′-azobis (2,4,4-trimethylpentane); dimethyl 2,2′-azobis (2-methylpropionate), dimethyl-2,
Azo ester compounds such as 2-azobisisobutyrate; azo acid compounds such as 4,4'-azobis (4-cyanopentanoic acid); 2,2'-azobis (2-aminodipropane) dihydrochloride; '-Azobis (N, N'-dimethyleneisobutylamidine), 2,
Amidine compounds such as 2′-azobis (N, N′-dimethyleneisobutylamidine) and 2,2′-azobis (N, N′-dimethyleneisobutylamidine) dihydrochloride; and peroxides such as sodium bisulfite Redox initiators and the like in combination with reducing agents can be used. These initiators can be used alone or in combination of two or more.

The amount (total amount) of the polymerization initiator used is 0.01 to 30 parts by weight, preferably 0.05 to 20 parts by weight, based on 100 parts by weight of the total amount of the monomers. If the amount is less than 0.01 parts by weight, a long time is required for polymerization, and the productivity is deteriorated. If it exceeds 30 parts by weight, aggregates increase, which is not preferable. The polymerization temperature and the polymerization time can be arbitrarily selected depending on the polymerization method and the type of the polymerization initiator to be used, but usually, the polymerization temperature is about 30 to 90 ° C., and the polymerization time is about 0.5 to 20 hours. .

The (meth) acrylate-based copolymer used in the present invention may be a copolymer (random copolymer or block copolymer) obtained by using the above-mentioned monomers in combination. Examples of particularly preferable polymers include 2-ethylhexyl acrylate-styrene copolymer, lauryl acrylate-styrene copolymer, stearyl acrylate-styrene copolymer, and tridodecyl acrylate-styrene copolymer. Polymer, 2-ethylhexyl methacrylate-styrene copolymer, lauryl styrene methacrylate copolymer, alkyl acrylate-2-ethylhexyl methacrylate-styrene copolymer, 2-ethylhexyl methacrylate-methoxypolyethylene glycol monoacrylate Methacrylate copolymer and the like. These copolymers are desirable because of their excellent high-temperature durability and excellent binding power and binding durability.

Further, it is possible to form a crosslink in the (meth) acrylate copolymer using a crosslinker in order to increase the binding force and the binding durability as a binder. As a method of forming a cross-link, a method of polymerizing using a monomer mixture to which a cross-linking agent is added, a method of adding a cross-linking agent and an initiator to a copolymer latex obtained by polymerization, and reacting the same are employed.

Specific examples of the crosslinking agent include benzoyl peroxide, dichlorobenzoyl peroxide, dicumyl peroxide, di-tert-butyl peroxide,
2,5-dimethyl-2,5-di (peroxidebenzoate) hexyne-3,1,4-bis (tert-butylperoxyisopropyl) benzene, lauroyl peroxide, tert-butylperacetate, 2,5-dimethyl -2,5-di (tert-butylperoxy) hexyne-3,2,5-trimethyl-2,5-di (ter
t-butylperoxy) hexane, tert-butylperbenzoate, tert-butylperphenylacetate, tert-butylperisobutyrate, tert
-Butyl per-sec-octoate, tert-butyl perpivalate, cumyl perpivalate, tert-
Peroxide-based crosslinking agents such as butyl perdiethyl acetate; azo compounds such as azobisisobutyronitrile and dimethylazoisobutyrate; dimethacrylate compounds such as ethylene diglycol dimethacrylate and diethylene glycol dimethacrylate; trimethylolpropane trimethacrylate Trimethacrylate compound; polyethylene glycol diacrylate, 1,3
Crosslinkable monomers such as diacrylate compounds such as -butylene glycol diacrylate; triacrylate compounds such as trimethylolpropane triacrylate; divinyl compounds such as divinylbenzene. Among these crosslinking agents, it is preferable to use crosslinking monomers such as dimethacrylate compounds such as ethylene glycol dimethacrylate and divinyl compounds such as divinylbenzene. The amount of the crosslinking agent varies depending on the reaction conditions and the type of the monomer, but is usually 0.05 to 30 parts by weight, preferably 0.5 to 15 parts by weight, per 100 parts by weight of the monomer component.

The (meth) acrylate copolymer used in the present invention is used as particles.
It may be spherical, irregular or irregular, and is not particularly limited, but its average particle size is usually 0.005 to 1
000 μm, preferably 0.01 to 100 μm, particularly preferably 0.02 to 50 μm. If the average particle size is too large, when used as a battery binder, it becomes difficult to contact the electrode active material, and the internal resistance of the electrode increases.
If it is too small, the necessary amount of the binder becomes too large, and the surface of the active material is covered. The “average particle diameter” here is a value obtained by measuring the major axis of 20 polymer particles in a transmission electron micrograph and calculating the average value.

In the present invention, a polymer containing a polymer other than the above-mentioned (meth) acrylate-based copolymer (hereinafter referred to as “other polymer”) can be used in combination. Various characteristics can be imparted to the electrode by appropriately selecting other polymers used in combination. Examples of the other polymer used in combination include a water-insoluble polymer (hereinafter, simply referred to as a water-insoluble polymer) and a water-soluble polymer other than the above-mentioned (meth) acrylate-based copolymer.

Specific examples of the water-insoluble polymer include polytetrafluoroethylene, polyvinylidene fluoride,
So-called water-repellent polymers having a very low affinity for water, such as fluoropolymers such as fluororubber and fluororesin, and polyolefins such as polyethylene and polypropylene; butadiene polymers, isoprene polymers, styrene-1,3
-Homopolymers or copolymers of conjugated diene monomers, such as butadiene copolymer, styrene-isoprene copolymer, styrene-1,3-butadiene-isoprene copolymer, and polystyrene-polybutadiene block copolymer. Elastomers and hydrides thereof; and the like. Above all, the above-mentioned effect of enhancing the binding force of the (meth) acrylate copolymer is remarkable in combination with a homopolymer or a copolymer of a conjugated diene monomer, and particularly in combination with a fluorine-containing polymer. Has a very remarkable effect. In addition, by using a fluorine-containing polymer in combination, an effect of suppressing an increase in internal pressure due to charging and discharging after manufacturing the battery can be obtained.

Specific examples of the water-soluble polymer include cellulosic polymers such as carboxymethylcellulose, methylcellulose and hydroxypropylcellulose; polyacrylates such as sodium polyacrylate; polyvinyl alcohol; polyethylene oxide; polyvinylpyrrolidone; Or a saponified product of a copolymer of acrylate and vinyl acetate, a saponified product of maleic anhydride or a copolymer of maleic acid or fumaric acid and vinyl acetate, modified polyvinyl alcohol, modified polyacrylic acid,
Gelatin and the like. By using the water-soluble polymer, the applicability in applying the composition containing the binder and the active material to the current collector in the production of the electrode is improved.

The amount of the other polymer used is usually 20 to 99% by weight, preferably 40% by weight, based on the total weight of the binder (the total weight of the solid content of the copolymer and the other polymer).
-95% by weight, more preferably 55-90% by weight. When a water-insoluble polymer and a water-soluble polymer are used in combination, the ratio of both (water-insoluble / water-soluble) (weight ratio)
From the viewpoint of the balance between the two characteristics, usually 100: 0 to 1
0:90, preferably 100: 0 to 20:80, more preferably 80:20 to 30:70.

In the present invention, the binder containing the above-mentioned (meth) acrylate-based copolymer is an active material 1
With respect to 00 parts by weight, usually 0.05 to 20.0 parts by weight,
Preferably, it is used in an amount of 0.1 to 10.0 parts by weight. If the amount of the binder is too small, the force for binding the active material to the current collector is insufficient, and the active material may fall off and the capacity of the battery may be reduced. On the other hand, if the amount of the binder is too large, the battery characteristics deteriorate, which is not preferable.

1-2) Conductive Material A conductive material can be added to the active material as needed. Examples of the conductive material include nickel powder, cobalt oxide, titanium oxide, and carbon. Examples of carbon include acetylene black, furnace black, graphite, carbon fiber, and fullerenes. When the conductive material is used, the amount of the conductive material is usually from 0.2 to 15% based on 100 parts by weight of the active material.
0 parts by weight.

1-3) Current Collector Specific examples of the metal current collector include a punching metal, an expanded metal, a wire mesh, a foamed metal, a sintered metal fiber fiber, and the like.

1-4) Production of Negative Electrode The negative electrode of the nickel-metal hydride battery of the present invention is obtained by adding a conductive material, the above-mentioned (meth) acrylate-based copolymer binder to a hydrogen storage alloy, and then adding water or the like. In general, a paste prepared by kneading in the presence of a paste is applied to a metal current collector, dried, and press-molded. Alternatively, the paste is prepared by immersing the current collector in the paste and drying the paste. You can also.

The hydrogen storage alloy may be a commonly used one, for example, an AB ₅ type (rare earth type) such as LaNi ₅ ,
AB / A ₂ B type (titanium) such as TiNi and Ti ₂ Ni
And there is such as AB ₂ type, such as NrNi. In addition, L
LaNi ₂ Co ₃ , MmNi in which La of aNi ₅ is replaced by misch metal Mm and a part of Ni is replaced by Mn or Co
₄ Co, MmNi ₂ Co ₃ , or an alloy composition Mm (Ni, Mn, Co...) M (Al,
Cr ...) n.

2) Positive Electrode The positive electrode of the nickel-metal hydride battery of the present invention comprises nickel hydroxide and / or nickel oxyhydroxide, the above-mentioned (meth) acrylate-based copolymer binder, cobalt monoxide, cobalt dioxide and water. Conductive materials such as cobalt oxide and metallic cobalt, carboxymethylcellulose, methylcellulose, sodium polyacrylate,
A paste containing a normal binder component such as polytetrafluoroethylene is applied to a metal base having a net-like or plate-like shape made of nickel, stainless steel, nickel-plated resin, etc., dried, and then press-molded. It is.

3) Separator The separator may be any of those used in alkaline secondary batteries. Examples thereof include polyethylene nonwoven fabric, polypropylene nonwoven fabric, polyamide nonwoven fabric and those obtained by subjecting them to hydrophilic treatment.

4) Electrolyte Solution Examples of the electrolyte solution include a potassium hydroxide aqueous solution and a solution obtained by adding sodium hydroxide and / or lithium hydroxide to a potassium hydroxide aqueous solution. 5) Nickel-metal hydride battery The nickel-metal hydride battery of the present invention is one in which the above-described positive electrode, negative electrode, separator and electrolyte are sealed in a metal container according to a conventional method.

[0035]

According to the present invention, when forming at least one of the positive and negative electrodes, a (meth) acrylate copolymer having an alkali group having 6 or more carbon atoms is used as a binder, so that it can be used at a high temperature. A nickel-metal hydride battery having excellent durability and having a small decrease in battery capacity as the charge-discharge cycle progresses can be obtained.

[0036]

The present invention will be described below in more detail with reference to examples. The particle diameter of the polymer is a value calculated by measuring the major axis of each of 20 particles in a transmission electron micrograph and calculating the average value. Example 1 Preparation of copolymer 400 parts by weight of ion-exchanged water, 55 parts by weight of styrene, 120 parts by weight of 2-ethylhexyl acrylate, 3 parts by weight of sodium dodecylbenzenesulfonate (surfactant; hereinafter referred to as DBS) and potassium persulfate 2.75 parts by weight (polymerization initiator; hereinafter referred to as KPS) were stirred and mixed, and
A monomer emulsion for step polymerization was obtained.

On the other hand, 70 parts by weight of ion-exchanged water was added to the reactor, 2 parts by weight of DBS was added, 5 parts by weight of styrene was further added, and the mixture was stirred to obtain an emulsion-dispersed monomer emulsion for the first-stage polymerization. Was. The temperature of the system was raised to 70 ° C. (first stage polymerization temperature), and 0.25 parts by weight of KPS was added to start polymerization. One hour after the start of the polymerization of the first-stage polymerization monomer emulsion, the temperature of the system was raised to 80 ° C. (second-stage polymerization temperature), and then the previously-prepared second-stage polymerization monomer emulsion was washed. Added over 3 hours. After the addition was completed, the polymerization was continued for another 2 hours. Polymerization conversion rate is 99%
Met. Next, after removing the residual monomer by a conventional method, the solid content concentration was adjusted to 40% by weight to obtain an acrylate copolymer A. The particle size of the copolymer A was 0.19 μm.

Production of Electrode (1) As a hydrogen storage alloy, a misch metal nickel alloy (A
B and ₅ type alloy) powder 100 parts by weight, the conductive material (carbon black, trade name: Ketjenblack EC) 1.0
Parts by weight, kneaded with 1.0 parts by weight of polytetrafluoroethylene (PTFE) dispersion (in terms of solids), 0.5 parts by weight of copolymer A (in terms of solids), and 0.5 part by weight of sodium carboxymethylcellulose Then, a paste (1) for a negative electrode was prepared. Obtained paste for negative electrode (1)
Was applied to a nickel-plated punching metal as a current collector, dried at 80 ° C., adjusted in thickness by a roll press, and then cut into a predetermined size to produce a negative electrode (1). No cracks were found in the negative electrode.

100 parts by weight of nickel hydroxide powder, 6 parts by weight of cobalt oxide, polytetrafluoroethylene (PTF)
3.0 parts by weight of the aqueous dispersion of E) (in terms of solids), 0.5 part by weight of the copolymer A (in terms of solids), and 0.5 part by weight of carboxymethylcellulose were kneaded to prepare a positive electrode paste (1). . The obtained positive electrode paste (1) was applied and impregnated into a foamed metal as a current collector, dried, and then cut into a predetermined size to prepare a positive electrode (1). No crack was found in the positive electrode.

Each of the obtained positive and negative electrodes (1) was 35%
Put into potassium hydroxide aqueous solution, at 60 ° C for 200 hours,
Next, a heat immersion test was performed at 100 ° C. for 24 hours, and when the active material and the conductive material were observed to fall, no fall was confirmed.

Production of Electrode (2) As a hydrogen storage alloy, a misch metal nickel alloy (A
B and ₅ type alloy) powder 100 parts by weight, the conductive material (carbon black, trade name: Ketjenblack EC) 1.0
By weight, 0.5 part by weight of the copolymer A (in terms of solid content) and 1.0 part by weight of carboxymethylcellulose sodium salt were kneaded to prepare a negative electrode paste (2). The obtained negative electrode paste (2) is applied to a nickel-plated punching metal as a current collector, dried at 80 ° C., adjusted in thickness by a roll press, cut into a predetermined size, and cut into a predetermined size. (2) was produced. No cracks were found in the negative electrode.

A positive electrode paste (2) was prepared by kneading 100 parts by weight of nickel hydroxide powder, 6 parts by weight of cobalt oxide, 1.0 part by weight of copolymer A (in terms of solid content), and 1.0 part by weight of carboxymethyl cellulose. . The obtained positive electrode paste (2) was applied and impregnated in a foamed metal as a current collector, dried, and then cut into a predetermined size to prepare a positive electrode (2). No crack was found in the positive electrode.

Each of the obtained positive and negative electrodes (2) was 35%
Put into potassium hydroxide aqueous solution, at 60 ° C for 200 hours,
Next, a heat immersion test was performed at 100 ° C. for 24 hours, and when the active material and the conductive material were observed to fall, no particular drop was confirmed.

Production of Electrode (3) As a hydrogen storage alloy, a misch metal nickel alloy (A
B and ₅ type alloy) powder 100 parts by weight, the conductive material (carbon black, trade name: Ketjenblack EC) 1.0
A negative electrode paste (3) was prepared by kneading 1.0 part by weight (in terms of solid content) of an aqueous dispersion of PTFE and 0.5 part by weight (in terms of solid content) of the copolymer A. The obtained negative electrode paste (3) is applied to a foamed metal as a current collector and impregnated with the paste.
After drying at 0 ° C., it was cut into a predetermined size to produce a negative electrode (3). No cracks were found in the negative electrode.

A mixture of 100 parts by weight of nickel hydroxide powder, 6 parts by weight of cobalt oxide, 1.0 part by weight of an aqueous dispersion of PTFE (in terms of solids), and 1.0 part by weight of copolymer A (in terms of solids) was kneaded. A paste (3) was prepared. The obtained paste for a positive electrode (3) was applied and impregnated into a foamed metal as a current collector, dried, and then cut into a predetermined size to prepare a positive electrode (3). No crack was found in the positive electrode.

Each of the obtained positive and negative electrodes (3) was 35%
Put into potassium hydroxide aqueous solution, at 60 ° C for 200 hours,
Next, a heat immersion test was performed at 100 ° C. for 24 hours, and when the active material and the conductive material were observed to fall, no particular drop was confirmed.

Production of Electrode (4) A misch metal nickel alloy (A
B and ₅ type alloy) powder 100 parts by weight, the conductive material (carbon black, trade name: Ketjenblack EC) 1.0
By weight, 1.0 part by weight (in terms of solid content) of the copolymer A was kneaded to prepare a negative electrode paste (4). The obtained negative electrode paste (4) is applied to a nickel-plated punching metal as a current collector, dried at 80 ° C., adjusted in thickness by a roll press, cut into a predetermined size, and cut into a predetermined size. (4) was produced. No cracks were found in the negative electrode.

A positive electrode paste (4) was prepared by kneading 100 parts by weight of nickel hydroxide powder, 6 parts by weight of cobalt oxide and 1.0 part by weight (in terms of solid content) of copolymer A. The obtained positive electrode paste (4) is applied to a punching metal as a current collector, dried at 80 ° C., adjusted to a predetermined thickness by a roll press, cut into a predetermined size, and cut into a predetermined size. (4) was produced. No crack was found in the positive electrode.

Each of the obtained positive and negative electrodes (4) was
% Potassium hydroxide aqueous solution, and subjected to a heat immersion test at 60 ° C. for 200 hours, and then at 100 ° C. for 24 hours.
When the active material and the conductive material were observed to fall, no particular loss was confirmed.

Production of Battery A nylon nonwoven fabric separator was sandwiched between the positive electrode (1) and the negative electrode (2), spirally wound, and inserted into an AA size battery can. Then, 31% potassium hydroxide was used as an electrolyte. An aqueous solution was injected to produce a sealed cylindrical battery (1) having a rated capacity of 1000 mAh. After the test battery was charged at 150% at 1 C, the charge-discharge cycle in which the cut-off voltage was 1.0 V and the battery was discharged at 1 C was repeated, and the number of discharges until the capacity reached 700 mAh was measured.

Example 2 400 parts by weight of ion-exchanged water, 45 parts by weight of styrene, 70 parts by weight of 2-ethylhexyl acrylate, 60 parts by weight of lauryl acrylate, 3 parts by weight of DBS, and 2.
75 parts by weight were stirred and mixed to obtain a second-stage polymerization monomer emulsion. On the other hand, 2 parts by weight of DBS was added to 70 parts by weight of ion-exchanged water, and 5 parts by weight of styrene was further added and stirred to obtain a monomer emulsion for first-stage polymerization emulsified and dispersed. . The temperature of the system was raised to 70 ° C. (first stage polymerization temperature), and 0.25 parts by weight of KPS was added to start polymerization.

One hour after the start of the polymerization of the first-stage polymerization monomer emulsion, the temperature of the system was raised to 80 ° C. (second-stage polymerization temperature), and then the previously adjusted second-stage polymerization monomer emulsion was prepared. Was added over 3 hours. After the addition was completed, the polymerization was continued for another 2 hours. The polymerization conversion was 99%. Next, after removing the residual monomer by a conventional method, the solid content concentration was adjusted to 40% by weight to obtain an acrylate copolymer B. The particle size of the copolymer B was 0.20 μm. An electrode was produced in the same manner as in Example 1 using the copolymer B, and a battery was produced.

Example 3 In a reactor, 470 parts by weight of ion-exchanged water, 50 parts by weight of styrene, 70 parts by weight of 2-ethylhexyl acrylate, 60 parts by weight of lauryl acrylate, 5 parts by weight of DBS, and KP
After adding 3.0 parts by weight of S and stirring and mixing, the temperature was decreased to 8%.
The temperature was raised to 0 ° C. to initiate polymerization. When the polymerization conversion reached 98%, the system was cooled. Next, after removing the residual monomer by a conventional method, the solid content concentration was adjusted to 40% by weight,
An acrylate copolymer C was obtained. The particle size of the copolymer C was 0.15 μm. An electrode was produced using Copolymer C in the same manner as in Example 1, and a battery was produced.

Example 4, Comparative Examples 1 to 3 Using the monomers shown in Table 1 below, in the same manner as in Example 1, an alkyl acrylate copolymer D and comparative (co) polymers ac to c Was prepared, and electrodes were prepared in the same manner as in Example 1 using the amounts used in Table 1, and further a battery was prepared.
Table 1 summarizes the evaluation results of the electrodes and batteries of Examples 1 to 4 and Comparative Examples 1 to 3.

[0055]

[Table 1]

From these results, it can be seen that when an electrode is prepared using a binder containing an acrylate copolymer having 6 or more carbon atoms according to the present invention, the high-temperature durability is excellent and the charge-discharge cycle proceeds. It can be seen that the nickel hydrogen battery has a small decrease in battery capacity.

Preferred Embodiment In the nickel-metal hydride battery of the present invention, that is, in the nickel-metal hydride battery using a hydrogen storage alloy as the negative electrode active material and nickel hydroxide or nickel oxyhydroxide as the positive electrode active material, At least one of them has at least 30% by weight of a repeating structural unit derived from an alkyl (meth) acrylate having an alkyl group bonded to a non-carbonyl oxygen atom of an ester bond having 6 or more carbon atoms and an aromatic vinyl compound. Preferred embodiments of a "nickel-metal hydride battery having a layer containing a (meth) acrylate copolymer having a repeating structural unit of 5% by weight or more and an active material" are summarized as follows.

(1) The (meth) acrylate-based copolymer has a repeating structure derived from an alkyl (meth) acrylate in which the alkyl group bonded to the non-carbonyl oxygen atom of the ester bond has 6 or more carbon atoms. Unit 30% by weight or more, preferably 45% by weight or more, more preferably 6% by weight
0% by weight or more, preferably 95% by weight or less, more preferably 90% by weight or less, and 5% by weight or more, preferably 10% by weight or more, more preferably 15% by weight or more of a repeating structural unit derived from an aromatic vinyl compound; It is preferably 70% by weight or less, more preferably 60% by weight or less, and still more preferably 50% by weight or less.

(2) The (meth) acrylic acid ester is a (meth) acrylic acid alkyl ester having 6 to 20 carbon atoms bonded to the non-carbonyl oxygen atom of the ester bond, and more preferably the above carbon number is 8 to 20 carbon atoms. 18 acrylic acid methacrylate. (3) An alkyl group having 6 or more carbon atoms is n-hexyl,
It is selected from ethylhexyl, isooctyl, isodecyl, lauryl, stearyl and tridecyl.

(4) The aromatic vinyl compound is styrene. (5) In addition to the units derived from the alkyl (meth) acrylate and the aromatic vinyl compound, the (meth) acrylate-based copolymer contains 20 units of units derived from other ethylenically unsaturated monomers. %, More preferably 10% by weight or less. (6) The (meth) acrylate copolymer is subjected to emulsion polymerization in the presence of 0.01 to 20 parts by weight of an anionic surfactant or a nonionic surfactant based on 100 parts by weight of the total amount of monomers. It is prepared by

(7) The (meth) acrylate-based copolymer is used in an amount of 0.05 to 100 parts by weight of the total amount of the monomers.
It is crosslinked with up to 30 parts by weight, more preferably 0.5 to 15 parts by weight of a crosslinking agent. (8) The (meth) acrylate-based copolymer has an average particle diameter of 0.005 to 1,000 μm, more preferably 0.01 to 100 μm, and particularly preferably 0.02 to 50 μm.
μm.

(9) The amount of the (meth) acrylate copolymer is usually 0.05 to 100 parts by weight of the active material.
To 20.0 parts by weight, more preferably 0.1 to 10.0 parts by weight. (10) The layer containing the (meth) acrylate copolymer and the active material further contains a water-soluble polymer and / or a water-insoluble polymer. (11) The amount of the water-soluble polymer and / or the water-insoluble polymer of the above (10) is more preferably 20 to 99% by weight, based on the total weight with the (meth) acrylate-based copolymer. Is 40 to 95% by weight, more preferably 55
~ 90% by weight.

(12) The active material is mixed with 0.2 to 10 parts by weight of a conductive material based on 100 parts by weight of the active material. (13) Both the positive electrode and the negative electrode have a layer containing the (meth) acrylate copolymer and an active material.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5H003 AA04 BB02 BB04 BB11 BC05 BD04 5H016 AA02 AA03 CC01 CC09 EE01 EE09 HH01 5H028 AA01 AA05 CC08 EE01 EE05 EE06 HH01

Claims (2)

[Claims] 1. A nickel-metal hydride battery using a hydrogen storage alloy as a negative electrode active material and nickel hydroxide or nickel oxyhydroxide as a positive electrode active material, respectively.
At least one of the positive and negative electrodes has at least 30% by weight of a repeating structural unit derived from an alkyl (meth) acrylate having an alkyl group bonded to a non-carbonyl oxygen atom in an ester bond having 6 or more carbon atoms, and aromatic vinyl. A nickel-metal hydride battery having a layer containing a (meth) acrylate copolymer having a repeating structural unit derived from a compound of 5% by weight or more and an active material. 2. A layer comprising the (meth) acrylate copolymer and an active material, wherein the layer further comprises a water-soluble polymer and / or
2. The nickel-metal hydride battery according to claim 1, further comprising a water-insoluble polymer.