Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Electrode
Reexamination Certificate
2001-03-27
2003-06-17
Weiner, Laura (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Electrode
C429S232000, C429S233000, C429S217000
Reexamination Certificate
active
06579645
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to an alkaline storage battery like a nickel-metal hydride battery, a hydrogen absorbing alloy electrode used as a negative electrode of the alkaline storage battery, and a hydrogen absorbing alloy used as the hydrogen absorbing alloy electrode, and is particularly characterized in that the hydrogen absorbing alloy for electrode used as the hydrogen absorbing alloy electrode and hydrogen absorbing alloy electrode are modified to improve high-rate discharge performance and charge and discharge cycle performance in the alkaline storage battery.
2. Description of the Related Art
A nickel-metal hydride battery has been conventionally known as one of alkaline storage batteries. Such a nickel-metal hydride battery has generally employed as its negative electrode a hydrogen absorbing alloy electrode.
As such a hydrogen absorbing alloy electrode for the alkaline storage battery, the one obtained by applying a paste prepared by mixing hydrogen absorbing alloy powder and a binding agent to a current collector and then drying the paste thereon has been generally utilized.
However, in the alkaline storage battery wherein the hydrogen absorbing alloy electrode as described above are used, the conductivity in the hydrogen absorbing alloy electrode is insufficient, thus charge and discharge performance at a high current is inferior. Further, the surface of the hydrogen absorbing alloy in the hydrogen absorbing alloy electrode is oxidized and deteriorated by the oxygen that appears in the positive electrode when the battery is overcharged, thus a discharge capacity is decreased gradually, and charge and discharge cycle performance is degraded.
Therefore, in Japanese Patent Laid-Open No. Shou61(1986)-163569, plating the surface of the hydrogen absorbing alloy powder with nickel or nickel alloy to improve the conductivity of hydrogen absorbing alloy powder and adhesion of the hydrogen absorbing alloy powder to the current collector has been proposed. In Japanese Patent Laid-Open No. Shou61(1986)-185863, covering the surface of the hydrogen absorbing alloy particles with carbon to prevent the oxidation of the hydrogen absorbing alloy by the oxygen that appears in the positive electrode when the battery is overcharged has been proposed. In Japanese Patent Laid-Open No. Shou63(1988)-266767, forming a porous conductive layer containing nickel and the like on the surface of the hydrogen absorbing alloy electrode to improve the conductivity of the hydrogen absorbing alloy electrode and prevent the oxidation of the hydrogen absorbing alloy in the hydrogen absorbing alloy electrode by the oxygen that appears in the positive electrode when the battery is overcharged has been proposed. In Japanese Patent Laid-Open No. Hei5(1993)-159798 and Japanese Patent Laid-Open No. Hei9(1997)-106817, plating the surface of the hydrogen absorbing alloy powder with metal containing particulates of water-repellent resin or fluorine compound to improve the conductivity of the hydrogen absorbing alloy powder and the adhesion of the hydrogen absorbing alloy powder to the current collector has been proposed.
Unfortunately however, even when the surface of the hydrogen absorbing alloy powder is plated with the nickel or nickel alloy, or the porous conductive layer containing the nickel and the like is formed on the surface of the hydrogen absorbing alloy electrode as mentioned above, the oxidation of the surface of the hydrogen absorbing alloy in the hydrogen absorbing alloy electrode by the oxygen that appears in the positive electrode when the battery is overcharged is not prevented fully, and the charge and discharge cycle performance is not fully improved.
There remain problems that the conductivity of the hydrogen absorbing alloy electrode is decreased, and the charge and discharge performance at a high current is degraded in a case where the surface of hydrogen absorbing alloy particles is covered with carbon as mentioned above.
There still remain problems that in a part where the above-mentioned water-repellent resin or fluorine compound exists, a contact between alkaline electrolyte solution and the hydrogen absorbing alloy powder is insufficient, charge and discharge reactivity in the hydrogen absorbing alloy electrode is decreased, and the discharge performance and the charge and discharge cycle performance at a high current is degraded in the case where the surface of the hydrogen absorbing alloy particles is plated with the metal containing water-repellent resin or fluorine compound as mentioned above.
SUMMARY OF THE INVENTION
An object of the present invention is to solve the above-mentioned problems in an alkaline storage battery wherein a hydrogen absorbing alloy electrode is employed as its negative electrode.
A first object of the present invention is to modify a hydrogen absorbing alloy for electrode and the hydrogen absorbing alloy electrode, to improve conductivity of the hydrogen absorbing alloy electrode.
A second object of the present invention is to modify the hydrogen absorbing alloy for electrode and the hydrogen absorbing alloy electrode, to prevent fully the hydrogen absorbing alloy from oxidation by oxygen that appears in a positive electrode when the battery is overcharged.
A third object of the present invention is to prevent hydrogen absorbing alloy particles from falling away from a current collector in the hydrogen absorbing alloy electrode wherein an electrode material using the hydrogen absorbing alloy particles is adhered to the current collector.
A fourth object of the present invention is to improve a high-rate discharge performance and a charge and discharge cycle performance in the alkaline storage battery wherein the hydrogen absorbing alloy electrode is employed as its negative electrode.
A first hydrogen absorbing alloy for electrode according to the present invention is a hydrogen absorbing alloy for electrode containing hydrogen absorbing alloy particles, wherein a covering layer containing at least one of metal elected from nickel and cobalt, and carbon particles is formed on a surface of said hydrogen absorbing alloy particles.
The conductivity of the hydrogen absorbing alloy electrode is improved by at least one of the metal elected from the nickel and the cobalt in the covering layer formed on the surface of the hydrogen absorbing alloy particles when the hydrogen absorbing alloy electrode using the first hydrogen absorbing alloy is employed as the negative electrode of the alkaline storage battery. Further, the oxidation of the hydrogen absorbing alloy in the hydrogen absorbing alloy electrode is prevented by the carbon particles in the covering layer even in the case where the oxygen appears in the positive electrode when the battery is overcharged.
The high-rate discharge performance and the charge and discharge cycle performance of the alkaline storage battery are improved as the conductivity of the hydrogen absorbing alloy electrode is improved and the oxidation of the hydrogen absorbing alloy in the hydrogen absorbing alloy electrode by oxygen that appears in the positive electrode when the battery is overcharged is prevented as mentioned above.
In forming the covering layer containing at least one of the metal elected from the nickel and cobalt, and the carbon particles on the surface of the hydrogen absorbing alloy particles as mentioned above, various ways can be adopted. However, to form easily the covering layer without decrease of the performance of the hydrogen absorbing alloy, the covering layer is preferably formed by plating, and more preferably by electroless plating.
In forming the covering layer containing at least one of the metal elected from the nickel and cobalt, and the carbon particles on the surface of the hydrogen absorbing alloy particles as mentioned above, when the thickness of the above-mentioned metal part in the covering layer is too thin, the conductivity of the hydrogen absorbing alloy electrode is not fully improved. On the other hand, when the th
Harada Yasuyuki
Maeda Reizo
Matsuura Yoshinori
Nohma Toshiyuki
Shinyama Katsuhiko
Armstrong Westerman & Hattori, LLP
Sanyo Electric Co,. Ltd.
Weiner Laura
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