Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Include electrolyte chemically specified and method
Reexamination Certificate
1998-07-30
2001-09-11
Brouillette, Gabrielle (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Include electrolyte chemically specified and method
C429S213000, C429S214000, C429S215000, C429S216000, C429S217000
Reexamination Certificate
active
06287723
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to an alkaline secondary battery comprising at least one anode electrode having an anode active material layer which contains an anode active material and a binder, and more particularly to an alkaline secondary battery improved by the specific binder for the anode electrode.
DESCRIPTION OF THE RELATED ART
An alkaline secondary battery comprises an electrolyte, at least one cathode electrode and at least one anode electrode, in which the electrolyte at least partially surrounds the cathode electrode and the anode electrode. Also there is optionally a separator which lies between the cathode electrode and the anode electrode. The cathode electrode has a cathode metallic collector and a cathode active material layer bound thereon. The cathode active material layer is formed by binding, with a cathode binder, a cathode active material such as nickel hydroxide or nickel oxy-hydroxide, a conductive material such as carbon, and additives such as cobalt powder. The anode electrode has an anode metallic collector such as punched metal, porous metallic plate, foamed metallic plate or sintered netlike metal fibeir plate, and an anode active material layer bound thereon. The anode active material layer is formed by binding, with an anode binder, an anode active material such as a hydridable alloy or a cadmium alloy, and a conductive material such as carbon, nickel powder or the like. The anode electrode is generally produced by blending the anode active material, the conductive material, the anode binder and water to obtain a paste, followed by spreading the paste on the anode metallic collector, and then drying it. It is necessary that the anode binder is a polymer capable of strongly binding the collector, the anode active material and the conductive material.
A water-insoluble polymer is usually preferred as the anode binder. Examples of water-insoluble polymers are fluorine-containing polymers such as poly-(tetrafluoroethylene) (=PTFE); ethylene-propylene-diene rubber (=EPDM), styrene-ethylene-butene-styrene copolymer (=SEBS) and the like. Additionally a water-soluble polymer may be used with the above water-insoluble polymer. Examples of water-soluble polymers are polyvinylalcohol, poly-(acrylic acid salt), water-soluble cellulose derivatives, poly-(ethylene glycol), poly-(vinyl pyrrolidone) and the like (see the Japanese unexamined patent publications of JP-A-03-283362, JP-A-04-1 21958, JP-A-04-206345, JP-A-04-272656, JP-A-06-140033, and JP-A-09-63589).
These anode binders, however, do not give sufficient binding between the collector and the anode active material layer resulting in the anode active material layer peeling from the anode collector overtime by repeat of charge and discharge. Thus properties such as battery capacity are reduced.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an alkaline secondary battery having a battery capacity which remains stabilized over repeated cycles of charge and discharge.
Another object of the present invention is to provide an anode electrode for the alkaline secondary battery having an anode active material layer tightly bound on an anode collector.
Another object of the present invention is to provide a method of producing the above anode electrode for the alkaline secondary battery.
The objects of the present invention can be achieved by using an anode binder which comprises a nonionic polymer produced by an emulsion polymerization in the presence of a nonionic surfactant. The anode active material layer containing an anode active material, a conductive material and the like are tightly bound on the anode collector, thereby stabilizing the battery capacity even through repeated cycles of charge and discharge.
In one aspect of the present invention, there is provided an alkaline battery comprising an electrolyte, at least one cathode electrode and at least one anode electrode having an anode collector and an anode active material layer on the anode collector, in which the anode active material layer contains an anode active material and an anode binder which includes a nonionic polymer produced by emulsion polymerization of at least one nonionic monomer in the presence of a nonionic surfactant, and the cathode electrode and the anode electrode are essentially surrounded by an electrolyte.
In another aspect of the present invention, there is provided an anode electrode for a secondary battery comprising an anode collector and an anode active material layer supported on the anode collector, in which the anode active material layer contains an anode active material and an anode binder including a nonionic polymer produced by emulsion polymerization of at least one nonionic monomer in the presence of a nonionic surfactant.
In another aspect of the present invention, there is provided a method for producing an anode electrode for a secondary battery comprising the steps of blending an anode active material, an anode binder and water to obtain a paste; spreading the paste on a anode collector; and then drying the paste. The anode binder comprises a nonionic polymer produced by emulsion polymerization of at least one nonionic monomer in the presence of a nonionic surfactant
DETAILED DESCRIPTION OF THIS INVENTION
An anode electrode for a secondary battery comprises an anode collector and an anode active material layer supported on the anode collector. The anode active material layer contains an anode active material such as a hydridable alloy or a cadmium alloy, and an anode binder.
The preferred anode binder of the present invention comprises a nonionic polymer. The nonionic polymer may not substantially contain ionizable group, and has an electric conductivity of generally not more than 2000 &mgr;S/cm, preferably not more than 1000 &mgr;S/cm, more preferably not more than 500 &mgr;S/cm. The electric conductivity is evaluated by dispersing the nonionic polymer in water to obtain a 10% by weight polymer-content latex of the nonionic polymer, and measuring electric conductivity of the latex.
The nonionic polymer of the present invention is obtained by emulsion polymerization of at least one nonionic monomer in the presence of a nonionic surfactant.
The nonionic surfactant is preferably a polyoxyethylene alkyl ether such as polyoxyethylene lauryl ether, polyoxyethylene cetyl ether, polyoxyethylene stearyl ether or polyoxyethylene oleyl ether; polyoxyethylene alkyl aryl ether such as polyoxyethylene nonyl phenyl ether or polyoxyethylene octyl phenyl ether; polyethylene glycol fatty acid ester, polyethylene glycol phosphate; sorbitol fatty acid ester; fatty acid monoglyceride; polyglycerine fatty acid ester; propyleneglycol fatty acid ester; cane sugar fatty acid ester, polyoxyethylene-polyoxypropylene block copolymer; polyoxyethylene-polyoxypropylene alkyl ether; ethylene oxide derivative of alkyl phenol formalin condensate; polyoxyethylene glycerine fatty acid ester, polyoxyethylene hardened castor oil; polyoxyethylene sorbitol fatty acid ester; fatty acid alkanolamide; polyoxyethylene fatty acid amide; and the like. Polyoxyethylene alkyl aryl ether is preferable. The nonionic surfactant can be used either alone or in combination with a water soluble polymer. Alternatively, the water soluble polymer may be used alone. The water soluble polymer of the present invention includes gelatin, polyvinylpyrrolidone, poly-(sodium acrylate), or polyvinylalcohol having saponification value of not less than 75% and polymerization degree of not less than 700, and the like.
The anionic surfactant may be added to stabilize the emulsion polymerization. The amount of the anionic surfactant, based on the total solid amount of surfactant, should be not more than 10% by weight, preferably not more than 5% by weight. As the anionic surfactant, examples are alkyl aryl sulfonate such as dodecyl benzene sodium sulfonate, dodecyl phenyl ether sodium sulfonate or the like; sulfosuccinate such as dioctyl sodium sulfosuccinate, dihexyl sodium sulfosuccinate or the like; salt of fatt
Haneda Hidekazu
Inoue Toshihiro
Maeda Koichiro
Wada Kenji
Yamamoto Haruhisa
Birch & Stewart Kolasch & Birch, LLP
Brouillette Gabrielle
Martin Angela J.
Nippon Zeon Co. Ltd.
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