JP2001283853A - Binder composition of negative electrode for alkaline secondary battery and its use - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a binder, for use with manufacturing of a negative electrode for an alkaline secondary battery, that has such characteristics that a paste made by kneading hydrogen-storing alloy powder and a conductive material with it has little viscosity variation per hour, and bonds the hydrogen-storing alloy and the conductive material firmly with the collector, and therefore, that an alkaline secondary battery using the negative electrode thus made has little deterioration in capacity accompanying the progress of charge/discharge cycle. SOLUTION: Copolymer latex containing at least (a) 2.9 to 20 wt.% of an aromatic vinyl monomer unit, (b) 79,9 to 97 wt.% of an ethylenic unsaturated monocarboxylic estermonomer unit, and (c) 0.1 to 6 wt.% of an ethylenic unsaturated carboxylic acid monomer unit is included in the binder for the alkaline secondary battery.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a binder composition for producing a negative electrode of an alkaline secondary battery and its use, and more particularly to a binder composition comprising a copolymer latex used for producing a negative electrode of an alkaline secondary battery. A slurry for a negative electrode of an alkaline secondary battery comprising the binder composition, the hydrogen storage alloy powder, and an active material; a negative electrode of an alkaline secondary battery manufactured using the slurry; and an alkaline secondary battery having the negative electrode. Next battery.

[0002]

2. Description of the Related Art An alkaline secondary battery has a structure in which an electrode group produced through a separator between a positive electrode and a negative electrode is housed in a container together with an alkaline electrolyte. The positive electrode binds additives such as nickel hydroxide and nickel oxyhydroxide as active materials, carbon as conductive material, and cobalt powder with a binder,
Further, it is bonded to a metal current collector. The negative electrode is made of a hydrogen storage alloy, a conductive material such as nickel powder or carbon, or carboxymethyl cellulose (CM).
C) adding a viscosity modifier which is a water-soluble polymer such as a sodium salt and a binder composition which is a latex,
The slurry prepared by kneading is applied to a metal current collector such as a punching metal, a perforated metal plate, a foamed metal plate, a sintered metal fiber plate, and dried, so that the hydrogen storage alloy and the conductive material can be exchanged by a binder. , And further bound to a metal current collector.

[0003] The binder can sufficiently bind the components such as the current collector, the active material, and the conductive material to each other in order to sufficiently exhibit the battery characteristics of the active material after being incorporated in the battery. It is required to be a polymer.
As a binder, ethylene-propylene-
Water-insoluble polymers such as diene rubber (EPDM) and styrene-ethylene-butene-styrene (SEBS) have been proposed, and rubber-based latex such as styrene-butadiene-based latex has been proposed as a binder composition (particularly). Kaihei 1-253159, JP-A-4-206
346, JP-A-6-13080, JP-A-6-6088
2, JP-A-7-73874). However, EP
DM has a disadvantage that it has a weak binding force to a conductive material and requires a solvent recovery treatment since it must be used after being dissolved in an organic solvent. Styrene-butadiene-based latex has a strong binding force, but has a problem that chemical stability is insufficient due to having a carbon-carbon double bond in the main chain, and the styrene-butadiene-based latex is easily oxidized and deteriorated with the progress of the charge / discharge cycle. is there.

[0004] A paste using latex as a binder composition is applied to an electrode substrate at the time of battery production. However, if the slurry is kneaded for a long time, the viscosity of the slurry changes during the application, and the thickness of the electrode is reduced. Sometimes changed. If the electrode thickness varies, the battery capacity will decrease. For these reasons, there is a need for a binder that can produce a slurry with good stability and can provide a battery with excellent battery characteristics.

[0005]

In view of the situation in the prior art, the present inventors have developed a binder composition which can improve the viscosity stability of a slurry and can produce an alkaline secondary battery having excellent charge / discharge characteristics. As a result of studying to obtain, when using a latex of a copolymer obtained by polymerizing at least a certain ratio of an aromatic vinyl monomer, an ethylenically unsaturated monocarboxylic acid ester monomer and an ethylenically unsaturated carboxylic acid monomer, the viscosity change of the slurry is reduced. small,
In addition, the inventors have found that a hydrogen storage alloy and a conductive material can be firmly bound to a current collector, and that a battery having a small decrease in battery capacity as the charge / discharge cycle progresses can be obtained. Was.

[0006]

Thus, according to the present invention, there is provided, as a first invention, at least (a) 2.9 to 20% by weight of an aromatic vinyl monomer unit, and (b) an ethylenically unsaturated monocarboxylic acid. 79.9 to 97% by weight of ester monomer units and 0.1 to 6% by weight of (c) ethylenically unsaturated carboxylic acid monomer units.
(based on the total amount of (a), (b), and (c)). A binder composition for a negative electrode of an alkaline secondary battery is provided.

Further, as a second invention, there is provided a slurry for producing a negative electrode comprising the binder composition according to the first invention and a negative electrode active material, and a third invention is produced using the slurry according to the second invention. A negative electrode for an alkaline secondary battery is provided, and as a fourth invention, an alkaline secondary battery having the negative electrode according to the third invention is provided.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a binder composition, a slurry, a negative electrode, and an alkaline secondary battery according to the present invention will be sequentially described. 1) Binder composition The binder composition for a negative electrode of the alkaline secondary battery of the present invention comprises at least (a) an aromatic vinyl monomer unit of 2.9 to
20% by weight, (b) 79.9 to 97% by weight of ethylenically unsaturated monocarboxylic acid ester monomer units and (c) 0.1 to 6% by weight of ethylenically unsaturated carboxylic acid monomer units
[The amount of each monomer unit is based on the total amount of (a), (b) and (c).] Is a latex in which the copolymer is present in an emulsified state in water. This latex is obtained by emulsion polymerization of a monomer in the presence of a surfactant, and the monomer used for producing this latex has a total of 80% of the monomers giving the units (a) to (c). If it is at least% by weight, other ethylenically unsaturated monomers can be used in combination.

Examples of the aromatic vinyl monomer used in the production of such a latex include styrene, α-methylstyrene, β-methylstyrene, pt-butylstyrene, chlorostyrene and the like. Of these, styrene is preferred. . The amount of the aromatic vinyl monomer is 2.9 to 20% by weight, preferably 4.5 to 18% by weight based on the total amount of the monomers (a), (b) and (c). If the amount of the aromatic vinyl monomer is too small, the polymerization stability of the latex decreases. Conversely, if the amount is too large, the flexibility of the polymer decreases.

Examples of the ethylenically unsaturated monocarboxylic acid ester monomer include (meth) acrylic acid ester monomers and crotonic acid ester monomers.
Specific examples thereof include methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, n-amyl acrylate, isoamyl acrylate, n-hexyl acrylate, acrylic Acrylic esters such as 2-ethylhexyl acrylate, hydroxypropyl acrylate and lauryl acrylate; methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate Methacrylates such as, lauryl methacrylate, tridodecyl methacrylate, stearyl methacrylate; and

Methyl crotonate, ethyl crotonate, propyl crotonate, butyl crotonate, isobutyl crotonate, n-amyl crotonate, isoamyl crotonate, n-hexyl crotonate, 2-ethylhexyl crotonate, hydroxypropyl crotonate and the like (I.e., β-methyl acrylate).

Among the above ethylenically unsaturated monocarboxylic acid ester monomers, alkyl acrylates having an alkyl moiety having 1 to 12 carbon atoms, preferably 4 to 8 carbon atoms, are preferred. The amount of the ethylenically unsaturated monocarboxylic acid ester monomer is from 79.9 to 97% by weight, preferably 81.9% by weight, based on the total amount of the monomers (a), (b) and (c).
5 to 95% by weight. If these amounts are too small, the flexibility of the copolymer decreases, while if they are too large, the stability of the paste viscosity becomes insufficient.

Examples of the ethylenically unsaturated carboxylic acid monomers include ethylenically unsaturated monocarboxylic acids such as (meth) acrylic acid monomers such as acrylic acid, methacrylic acid and crotonic acid, and itaconic acid, fumaric acid and maleic acid. Ethylenically unsaturated dicarboxylic acids are mentioned.
Among the ethylenically unsaturated carboxylic acid monomers, ethylenically unsaturated mono- or dicarboxylic acids having 4 to 6 carbon atoms are preferred, and acrylic acid and methacrylic acid are particularly preferred. The amount of the ethylenically unsaturated carboxylic acid monomer is 0.1 to 6% by weight, preferably 0.5 to 5% by weight based on the total amount of the monomers (a), (b) and (c). If the amounts are too small, the stability of the slurry viscosity will be reduced. Conversely, if the amounts are too large, the electrolyte resistance will be reduced. Each of (a) an aromatic vinyl monomer, (b) an ethylenically unsaturated monocarboxylic acid ester monomer, and (c) an ethylenically unsaturated carboxylic acid monomer can be used alone or in combination of two or more.

If desired, the monomers (a), (b) and
In addition to (c), other ethylenically unsaturated monomers can be copolymerized. Specific examples of other ethylenically unsaturated monomers to be copolymerized include conjugated diene monomers such as 1,3-butadiene, isoprene, 2,3-dimethylbutadiene, and piperylene; acrylonitrile,
Nitrile group-containing monomers such as methacrylonitrile;
Acrylamide, N-methylolacrylamide, N-
Acrylamide monomers such as butoxymethylacrylamide; methacrylamide monomers such as methacrylamide, N-methylol methacrylamide, N-butoxymethylmethacrylamide; glycidyl acrylate;
Glycidyl group-containing monomers such as glycidyl methacrylate and allyl glycidyl ether; methacrylic acid-based monomers such as dimethylaminoethyl methacrylate and diethylaminoethyl methacrylate; and methacrylic acid-based monomers such as methoxypolyethylene glycol monomethacrylate. No. The amount of these optionally copolymerized monomers is 20% by weight or less, preferably 10% by weight or less of the total amount of all the monomers constituting the copolymer.

Each of the above monomers is emulsion polymerized in the presence of a surfactant. As the surfactant, benzenesulfonates such as sodium dodecylbenzenesulfonate and sodium dodecylphenylethersulfonate; alkyl sulfates such as sodium lauryl sulfate and sodium tetradodecyl sulfate; sodium dioctyl sulfosuccinate, sodium dihexyl sulfosuccinate and the like Sulfosuccinates; fatty acid salts such as sodium laurate; polyoxyethylene lauryl ether sulfate sodium salt, polyoxyethylene nonylphenyl ether
Ethoxy sulfate salts such as tersulfate sodium salt; alkane sulfonate; alkyl ether phosphate sodium salt; polyoxyethylene allyl ether such as polyoxyethylene lauryl ether and polyoxyethylene nonyl phenyl ether; polyoxyethylene allyl glycidyl nonyl Reactive surfactants such as phenyl ether and polyoxyethylene allyl glycidyl nonyl phenyl ether sulfate are exemplified. The addition amount of these surfactants can be set arbitrarily,
Usually from 0.01 to 10 based on 100 parts by weight of the total amount of monomers.
It is about parts by weight.

The emulsion polymerization is carried out according to a conventional method. Among emulsion polymerization, seed polymerization is particularly preferred. At the time of emulsion polymerization, the method of adding the monomer may be any method such as batch polymerization, continuous addition, divisional addition, and the monomer is
It may be added after emulsification, or only a monomer may be added. Further, a hydrophilic organic solvent such as alcohol or ketone may be added to the polymerization system as needed.
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.
200 ° C., and the polymerization time is about 0.5 to 20 hours.

The polymerization initiator used in the emulsion polymerization includes ketone peroxides such as methyl ethyl ketone peroxide, methyl isobutyl ketone peroxide and cyclohexanone peroxide; di-t-butyl peroxide, t-butyl-α-cumyl peroxide, Mil peroxide,
Dialkyl peroxides such as 1,3-bis (t-butylperoxyisopropyl) benzene and 1,4-bis (t-butylperoxyisopropyl) benzene; acetyl peroxide, propionyl peroxide, isobutyryl peroxide, octanoyl Peroxide 3,5,
Diacyl peroxides such as 5-trimethylhexanoyl peroxide, decanoyl peroxide, lauroyl peroxide, benzoyl peroxide; t-butyl hydroperoxide, cumene hydroperoxide, diisopropylbenzene hydroperoxide, p-menthane hydroperoxide 2,5-dimethylhexane-2,5-
Hydroperoxides such as dihydroperoxide, 1,1,3,3-tetramethylbutyl hydroperoxide;
Di-2-ethylhexylperoxydicarbonate, diisopropylperoxydicarbonate, di-sec-
Peroxydicarbonates such as butylperoxydicarbonate and di-n-propylperoxydicarbonate; 1,1-bis-t-butylperoxy-3,3,5-
Peroxyketals such as trimethylcyclohexane, n-butyl-4,4-bis (t-butylperoxy) valerate, and 2,2-bis (t-butylperoxy) butane; t-butylperoxyacetate, t-butyl Organic peroxides such as alkyl peresters such as peroxyisobutyrate and t-butylperoxyoctoate; 2,2′-azobisisobutyronitrile, 2,2′-azobis (2,4-dimethyl) Valeronitrile), 2,2'-
Azobis (4-methoxy-2,4-dimethylvaleronitrile), 2,2'-azobis (2- (hydroxymethyl)
Azonitrile compounds such as propionitrile) 1,1-azobis (cyclohexane-1-carbonitrile);
2,2′-azobis (2-methylpropionamide) dihydrate, 2,2′-azobis (2-methyl-N- (1,1-
Bis (hydroxymethyl) ethyl) propionamide), 2,2′-azobis (2-methyl-N- (1,1-
Azoamide compounds such as bis (hydroxymethyl) -2-hydroxyethyl) propionamide); 2,2′-azobis (2-methylpropane) and 2,2′-azobis (2,4,4-trimethylpentane) Alkyl azo compound; 2,2'-azobis (2-methylpropionic acid)
Azoester compounds such as dimethyl and dimethyl-2,2-azobisisobutyrate; azoacid compounds such as 4,4′-azobis (4-cyanopentanoic acid); 2,2′-
Azobis (2-aminodipropane) dihydrochloride, 2,2′-azobis (N, N′-dimethyleneisobutylamidine), 2,2′-azobis (N, N′-dimethyleneisobutylamidine), 2,2 '-Azobis (N, N'
Amidine compounds such as -dimethyleneisobutylamidine) dihydrochloride; and the like.
In addition, persulfates such as potassium persulfate and ammonium persulfate used in ordinary emulsion polymerization; hydrogen peroxide and the like can also be used. The above polymerization initiators can be used alone or in combination of two or more. The amount of the polymerization initiator used is 0.0 with respect to 100 parts by weight of the total amount of the monomers.
It is 1 to 10 parts by weight, preferably 0.05 to 5 parts by weight. If the amount is less than 0.01 part by weight, a long time is required for polymerization, and the productivity is poor. If it exceeds 10 parts by weight, aggregates increase.

Further, in order to enhance the performance as a binder composition for a negative electrode, it is possible to crosslink the copolymer using a crosslinking agent during or after the polymerization. When a cross-linking agent is used, the amount of the cross-linking agent varies depending on the reaction conditions and the type of polymer, but is usually 30% by weight or less based on the amount of the copolymer. 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- Screw (tert
-Butylperoxyisopropyl) benzene, lauroyl peroxide, tert-butylperacetate,
2,5-dimethyl-2,5-di (tert-butylperoxy) hexyne-3,2,5-trimethyl-2,5-di (tert-butylperoxy) hexane, tert-
Butyl perbenzoate, tert-butyl perphenyl acetate, tert-butyl perisobutyrate,
tert-butyl per-sec-octoate, ter
t-butyl perpivalate, cumyl perpivalate, t
peroxide-based crosslinking agents such as tert-butyl perdiethyl acetate and azo compounds such as azobisisobutyronitrile and dimethylazoisobutyrate; dimethacrylate compounds such as ethylene diglycol dimethacrylate and diethylene glycol dimethacrylate; trimethylolpropanetri Cross-linking monomers such as trimethacrylate compounds such as methacrylate; diacrylate compounds such as polyethylene glycol diacrylate and 1,3-butylene glycol diacrylate; triacrylate compounds such as trimethylolpropane triacrylate; divinyl compounds such as divinylbenzene; Is exemplified. Among these crosslinking agents, crosslinking monomers such as dimethacrylate compounds such as ethylene glycol dimethacrylate and divinyl compounds such as divinylbenzene are preferred. Such a crosslinking agent is generally used in an amount of 0.05 to 30 parts by weight, preferably 0.5 to 10 parts by weight, based on 100 parts by weight of the monomer component.

The particle size of the polymer used in the present invention is usually 0.005 to 1,000 μm, preferably 0.01 to 10 μm.
0 μm, more preferably 0.05 to 10 μm. If the 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.

In an alkaline secondary battery using the binder composition of the present invention, in terms of battery characteristics, a polymer other than the above-described copolymer (hereinafter, referred to as “binder”) is used as the binder composition.
(Referred to as "other polymers"). Other polymers to be blended include fluorine-containing polymers such as polytetrafluoroethylene and polyvinylidene fluoride, and polyolefins such as polyethylene and polypropylene, and so-called water-repellent polymers having extremely low affinity for water; Elastomers such as conjugated diene-based monomer polymers or copolymers such as isoprene polymers, styrene-isoprene copolymers, styrene-1,3-butadiene-isoprene copolymers, and polystyrene-polybutadiene block copolymers; and hydrides thereof. Among them, the fluorine-containing polymer is particularly preferable because not only the effect of enhancing the binding force is remarkable, but also the effect of suppressing an increase in internal pressure due to charging and discharging of the battery is obtained.

Other polymers include cellulosic polymers such as carboxymethylcellulose, methylcellulose and hydroxypropylcellulose, and ammonium salts and alkali metal salts thereof, polyacrylates such as sodium polyacrylate, polyvinyl alcohol, polyethylene oxide, and the like. Highly hydrophilic polymers such as polyvinylpyrrolidone, copolymers of acrylic acid or acrylates and vinyl alcohol, maleic anhydride or copolymers of maleic acid or fumaric acid and vinyl alcohol, modified polyvinyl alcohol, modified polyacrylic acid, gelatin and the like. When a hydrophilic polymer is used, the applicability of applying a composition containing a binder and an active material to a current collector in the production of a negative electrode is improved.

The amount of the other polymer as described above is usually 10 to 400% by weight, preferably 20 to 300% by weight, more preferably 50 to 20% by weight, based on the copolymer.
0% by weight. When the water-repellent polymer and the hydrophilic polymer are used in combination, the weight ratio of the water-repellent polymer / hydrophilic polymer is usually 100/0 to 10/90, preferably 100/100, in consideration of the balance between the properties of both. / 0-2
0:80, more preferably 80/20 to 30/70.

2) Slurry and Negative Electrode The negative electrode for an alkaline secondary battery of the present invention is obtained by coating the current collector with the slurry of the present invention containing the binder composition, the hydrogen storage alloy powder and the conductive material. And a layer obtained by evaporating and drying the water. The negative electrode is usually prepared by applying a slurry prepared by kneading the binder composition, the hydrogen storage alloy powder, and a conductive material in the presence of water or the like to a metal current collector, drying, and press molding. . After immersing the metal current collector in the slurry, the metal current collector may be dried and press-molded.

The amount of the binder composition of the present invention containing the copolymer latex and another polymer is usually 0.0 as a solid based on 100 parts by weight of the hydrogen storage alloy.
It is 5 to 10 parts by weight, preferably 0.1 to 7 parts by weight.
The amount of the copolymer latex in the binder composition of the present invention is usually 0.01 to 6 parts by weight, preferably 0.05 to 6 parts by weight, based on 100 parts by weight of the hydrogen storage alloy.
4 parts by weight. Amount of copolymer latex (solid content)
If the amount is too small, the force for binding the hydrogen storage alloy to the current collector is insufficient, and the alloy may fall off and reduce the capacity of the battery. Conversely, if the amount is too large, the battery characteristics tend to decrease.

The hydrogen storage alloy used as the active material of the negative electrode may be one generally used for an alkaline secondary battery. For example, an AB ₅ type (rare earth type) such as LaNi ₅ ,
and AB / A ₂ B type (titanium type) such as ini, Ti ₂ Ni, ZrNi type, MgNi type and the like. In addition, LaNi
MnNi ₂ Co ₃ , MmNi ₄ Co in which La of No. ₅ was replaced with Mish metal Mm and a part of Ni was replaced with Mn or Co
And an alloy composition Mm (N
i, Mn, Co, etc.) m (Al, Cr, etc.) n.

As the conductive material used in combination with the active material,
For example, nickel powder, cobalt oxide, titanium oxide, carbon, and the like can be given. As carbon,
Examples include acetylene black, furnace black, graphite, carbon fiber, and fullerenes. Preferably, acetylene black, furnace black,
Particularly, among furnace blacks, Ketjen Black manufactured by Ketjen Black International is preferred. The amount of the conductive material used is 0.2 to 10.0 parts by weight based on 100 parts by weight of the hydrogen storage alloy. If the amount is less than 0.2 parts by weight, the conductivity is low, and the capacity of the secondary battery when charged and discharged at a high rate may be reduced. The metal current collector is not particularly limited as long as it is generally used for an alkaline secondary battery electrode, and examples thereof include punching metal, expanded metal, wire netting, foamed metal, and reticulated metal fiber sintered body. Can be.

3) Battery The alkaline secondary battery of the present invention includes a negative electrode manufactured using the above binder. That is, it has a structure in which an electrode group configured by interposing a separator between the positive electrode and the negative electrode is housed in a container together with an alkaline electrolyte. The positive electrode of the alkaline secondary battery of the present invention may be the same as that of a general alkaline secondary battery, and is usually a nickel oxide such as nickel hydroxide, nickel oxyhydroxide, nickel oxide, cobalt monoxide, trioxide. A paste containing a conductive material such as cobalt dioxide, cobalt hydroxide, and metal cobalt and, if necessary, a binder such as carboxymethylcellulose, methylcellulose, sodium polyacrylate, and polytetrafluoroethylene, is plated with nickel, stainless steel, and nickel. It is applied to a metal substrate having a net-like or plate-like shape made of resin or the like, dried, and then formed using a roll press.

As the separator, those used for general alkaline secondary batteries are used, and examples thereof include polyethylene nonwoven fabric, polypropylene nonwoven fabric, polyamide nonwoven fabric and those subjected to hydrophilic treatment.
Examples of the electrolytic 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.

[0029]

EXAMPLES Hereinafter, the binder composition, the negative electrode, and the alkaline secondary battery of the present invention will be specifically described with reference to examples. Example 1 Production of copolymer latex In a reactor equipped with a stirrer, 50 parts by weight of ion-exchanged water and 0.2 part by weight of sodium dodecylbenzenesulfonate were added, and then 5 parts by weight of styrene were added, followed by stirring to obtain an emulsion. This emulsion was heated to 70 ° C. while stirring.
To this emulsion, 0.5 parts by weight of ammonium persulfate was added to start the first stage polymerization. One hour after the start of polymerization,
The temperature was raised to 80 ° C., and as an emulsion for the second stage polymerization, 100 parts by weight of ion-exchanged water, 85 parts by weight of 2-ethylhexyl acrylate, 9 parts by weight of styrene, 1 part by weight of acrylic acid,
An emulsion obtained by mixing and stirring 2 parts by weight of ethylene glycol dimethacrylate, 1 part by weight of sodium dodecylbenzenesulfonate and 1.5 parts by weight of ammonium persulfate was added over 3 hours. After the addition of the second-stage polymerization emulsion, the temperature was further maintained at 80 ° C., and the mixture was stirred for 2 hours. Then, the heating device was removed, and the reaction system was cooled to room temperature. At this time, the monomer consumption was about 100% by weight. After cooling, unreacted monomers were removed. Then, p with an aqueous solution of potassium hydroxide
H was adjusted to 6.5 and the solid content concentration was adjusted to 35% by weight to obtain a binder latex A.

Manufacture of negative electrode A misch metal nickel alloy (A
And B ₅ alloy) powder 100 parts by weight of conductive material (trade name: Ketjenblack EC) 2.0 parts by weight, 1.5 parts by weight dispersion solids polytetrafluoroethylene, binders Latex A solid 1 A paste was prepared by kneading 1.5 parts by weight of 1.5 parts by weight of carboxymethylcellulose. The viscosity stability test of this paste was performed as follows. That is, the paste was allowed to stand in an atmosphere of 25 ° C. for 1 hour, kneaded for 10 minutes, and then the viscosity was measured using a BM type viscometer. Further, the mixture was allowed to stand at 25 ° C. for 1 hour and kneaded for 10 minutes, and the viscosity was measured. Next, the mixture was allowed to stand for 24 hours, stirred for 10 minutes, and then the viscosity was measured. After an additional 24 hours (ie, 50 hours after making the paste)
After 48 hours (ie, 74 hours after the preparation of the paste), the same operation was performed, and the viscosity was measured. Table 1 shows the results of the viscosity change.

Next, a binding test was performed on the electrode prepared using the paste subjected to the viscosity measurement after 74 hours as follows. The paste was applied to a nickel-plated punching metal serving as a current collector, dried at 80 ° C., adjusted in thickness by a roll press, and cut into a predetermined size to produce two negative electrodes. At this time, no crack was found in the electrode. One of the obtained negative electrodes was subjected to an electrolyte resistance test. That is, the obtained electrode plate is
It was immersed in a 6N aqueous KOH solution at 70 ° C. for 72 hours, and the falling off of the active material was observed. Table 1 shows the results.

Preparation of Battery 100 parts by weight of nickel hydroxide powder, 6 parts by weight of cobalt oxide, 3.0 parts by weight of polytetrafluoroethylene dispersion (as solid content), and 1.0 part by weight of carboxymethyl cellulose are kneaded and paste. Was prepared. The obtained paste was applied and impregnated on a foamed metal as a current collector, dried, and then cut into a predetermined size to produce a positive electrode.

[0033] Between the positive electrode and the negative electrode (the remaining one of the previously obtained negative electrodes), in combination with a separator made of nylon non-woven fabric, spirally wound and inserted into a battery can, and then 31 wt. % Potassium hydroxide aqueous solution,
A sealed cylindrical battery having a nominal capacity of 1,000 mAh was produced. After the test battery was charged at 1 C by 150%, the charge / discharge cycle in which the cut-off voltage was 1.0 V and the battery was discharged at 1 C was repeated. The capacity at the time of the 500th discharge is 775 mA
h.

Example 2 and Comparative Examples 1 and 2 A copolymer latex was prepared in the same manner as in Example 1 except that the monomers, initiators and emulsifiers shown in Table 1 were used.
Further, a paste, a negative electrode, and an alkaline secondary battery were produced, and a test was performed in the same manner as in Example 1. Table 1 shows the results.

[0035]

[Table 1]

The symbols in Table 1 are as follows. 2HEA: 2-ethylhexyl acrylate St: styrene AA: acrylic acid MMA: methyl methacrylate DBS: sodium dodecylbenzenesulfonate AIBN: azobisisobutyronitrile APS: ammonium persulfate EGDMA: ethylene glycol dimethacrylate

[0037]

The paste obtained by kneading the hydrogen-absorbing alloy powder and the conductive material using the binder composition of the present invention when producing the negative electrode has a small change in viscosity over time, and has a small effect on the hydrogen-absorbing alloy and the conductive property. An alkaline secondary battery having a negative electrode obtained by firmly binding a material to a current collector has a characteristic that a decrease in battery capacity accompanying a progress of a charge / discharge cycle is small.

Continuing from the front page (72) Inventor Toshihiro Inoue 2-1-1, Yakko, Kawasaki-ku, Kawasaki-ku, Kanagawa Prefecture F-term in the Zeon Corporation General Development Center (reference) 5H050 AA07 AA14 AA19 BA11 BA14 CA03 CB16 DA03 DA11 EA28 HA01

Claims (4)

[Claims] 1. At least (a) 2.9 to 20% by weight of an aromatic vinyl monomer unit, (b) 79.9 to 97% by weight of an ethylenically unsaturated monocarboxylic acid ester monomer unit and (c) an ethylenically unsaturated unit Carboxylic acid monomer units 0.1 to
6% by weight [the amount of each monomer unit is (a), (b),
(based on the total amount of (c))]. A binder composition for a negative electrode of an alkaline secondary battery, comprising a latex of a copolymer. 2. A slurry for producing a negative electrode, comprising the binder composition according to claim 1 and a negative electrode active material. 3. A negative electrode for an alkaline secondary battery produced by using the slurry according to claim 2. 4. An alkaline secondary battery having the negative electrode according to claim 3.