Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Electrode
Reexamination Certificate
2002-04-16
2004-12-28
Weiner, Laura (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Electrode
C429S232000, C429S231500, C429S233000, C429S206000, C427S126100
Reexamination Certificate
active
06835497
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an alkaline storage battery such as a nickel-metal hydride battery, a nickel-cadmium battery, and the like, and to a nickel electrode for alkaline storage battery used for a positive electrode of the lkaline storage battery as described above, and is particularly characterized in that charge/discharge cycle performance of the alkaline storage battery under high temperature conditions is improved upon bettering the nickel electrode for alkaline storage battery formed by applying a paste containing active material particles composed of nickel hydroxide to a conductive substrate and then drying the paste on the conductive substrate.
2. Description of the Related Art
A conventional alkaline storage battery such as a nickel-metal hydride battery and nickel-cadmium battery, has used as its positive electrode a nickel electrode for alkaline storage battery using nickel hydroxide as an active material.
In the above-mentioned nickel electrode for alkaline storage battery, conductivity of the nickel hydroxide used as the active material is low. Accordingly, a sintered nickel electrode formed by impregnating a substrate prepared by filling nickel powder into a conductive substrate such as porous steel sheet and the like and then sintering the conductive substrate having the nickel powder filled therein, with nickel hydroxide as the active material has been conventionally used.
However, in such sintered nickel electrode, close adherence between particles of the nickel powder is weak. Accordingly, the nickel powder drops out easily when the substrate having high degree of porosity is used. Therefore, the maximum porosity of such substrate is 80% in actual conditions, and hence, the nickel hydroxide as the active material is not sufficiently filled, thus an alkaline storage battery having a large capacity was hardly attained.
Further, in the above-mentioned sintered nickel electrode, substrate including the porous steel sheet is used, thus, filling density of the active material is generally small. In addition, a pore diameter of the nickel powder formed by sintering is generally small, for example, not more than 10 &mgr;m. Thus, in filling the active material into the substrate, solution impregnating method in which laborious work is repeatedly performed for cycles must be taken, thereby degrading productivity.
Therefore, a paste type nickel electrode for alkaline storage battery formed by applying a paste which is obtained by mixing the active material particles composed of nickel hydroxide with an aqueous solution as a binding agent such as methyl cellulose to a conductive substrate having the high degree of porosity such as foamed nickel and drying said paste has been used.
In such paste type nickel electrode for alkaline storage battery, the conductive substrate having the porosity of not less than 95% can be used. Accordingly, a large number of active materials can be filled into the conductive substrate, thus the alkaline storage battery having the large capacity is attained, and the active materials can be easily filled into the conductive substrate, thereby improving the productivity.
However, in such paste type nickel electrode for alkaline storage battery, when the conductive substrate having the high degree of porosity is used to fill the large number of active materials therein, current collectivity of the conductive substrate is degraded, thereby reducing the utilization efficiency of the active materials.
Therefore, in recent years, in such paste type nickel electrode for alkaline storage battery, a method in which metal cobalt or a cobalt compound composed of a cobalt oxide or a hydroxide as a conductive agent are added to the above-mentioned active material particles composed of nickel hydroxide, then the above-mentioned metal cobalt or the cobalt compound are oxidized to &bgr;-CoOOH which is cobalt oxyhydroxide by charge, to increase the conductivity of the electrode, thus to improve the utilization efficiency of the active materials has been used.
However, even in a case in which the metal cobalt or the cobalt compound as the conductive agent are added to the active material particles composed of nickel hydroxide, there still have remained problems that when the paste type nickel electrode for alkaline storage battery is used as the positive electrode of the alkaline storage battery and is charged under high temperature conditions, an oxygen overvoltage in the positive electrode is decreased, thus in addition to a charge reactivity in which nickel hydroxide is oxidized to nickel oxyhydroxide, a side reaction in which an oxygen evolution reactivity occurs and hence, charge characteristics is decreased have occurred.
In this connection, Japanese Laid-Open No. Shou 57-187869 proposes to add at least one of metal titanium, titanium oxide, and titanium hydroxide to the active material composed of nickel hydroxide as well as to use an alkaline electrolyte solution containing lithium ion in order to improve charge/discharge efficiency of the alkaline storage battery upon improving the utilization efficiency of the nickel electrode.
However, in the alkaline storage battery in which at least one of metal titanium, titanium oxide, and titanium hydroxide is added to the active material composed of nickel hydroxide and alkaline electrolyte solution containing lithium ion is used, there have remained problems that the current collectivity of the electrode is degraded, and sufficient discharge capacity is not attained.
SUMMARY OF THE INVENTION
An object of the present invention is to increase current collectivity and to improve utilization efficiency of active material of a nickel electrode for alkaline storage battery formed by applying paste containing active material particles composed of nickel hydroxide to a conductive substrate and then drying the paste on the conductive substrate.
Another object of the present invention is, in a case in which an alkaline storage battery using as its positive electrode the above-mentioned nickel electrode for alkaline storage battery is charged and discharged under high temperature conditions, to prevent discharge capacity of the alkaline storage battery from gradually decreasing and to improve charge/discharge cycle performance under high temperature conditions.
The nickel electrode for alkaline storage battery of the present invention is formed by applying the paste containing the active material particles composed of nickel hydroxide to the conductive substrate and then drying the paste on the conductive substrate, wherein a conductive layer consisting of sodium-containing cobalt oxide is formed on a surface of the above-mentioned active material particles, and titanium powder and/or titanium compound powder is added to the active material particles.
Further, when the conductive layer consisting of sodium-containing cobalt oxide is formed on the surface of the active material particles composed of nickel hydroxide as the nickel electrode for alkaline storage battery of the present invention, the current collectivity inside the electrode becomes higher, thus the utilization efficiency of the active material is improved, because electrical conductivity of the sodium-containing cobalt oxide is higher than that of metal cobalt or cobalt compound.
When charge/discharge is performed to the alkaline storage battery using as its positive electrode the nickel electrode for alkaline storage battery under high temperature conditions, the sodium-containing cobalt oxide is prevented from being reduced to the cobalt hydroxide during discharge and dissolving into an alkaline electrolyte solution of the alkaline storage battery.
In addition, when the titanium powder and/or titanium compound powder is added to the active material particles which are composed of nickel hydroxide, and on which the conductive layer consisting of sodium-containing cobalt oxide is formed, the speed for which the cobalt hydroxide dissolves into the alkaline electrolyte solution and deposits is de
Fujitani Shin
Ogasawara Takeshi
Tokuda Mitsunori
Yano Mutsumi
Weiner Laura
Westerman Hattori Daniels & Adrian LLP
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