Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Electrode
Reexamination Certificate
2001-06-15
2003-11-18
Gulakowski, Randy (Department: 1746)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Electrode
Reexamination Certificate
active
06649304
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a rechargeable battery whose cathode principally comprising a nickel hydroxide (this rechargeable battery will be hereinafter referred to as a nickel series rechargeable battery) and a process for producing said nickel series rechargeable battery. More particularly, the present invention relates to a nickel series rechargeable battery having a high energy density, excelling in resistance to overcharge, and having a prolonged cycle life, wherein the cathode comprises an active material principally comprising a specific amorphous phase-bearing nickel hydroxide particulate having a prolonged lifetime and which has a high utilization efficiency of the active material (the “utilization efficiency of the active material” will be hereinafter referred to as “active-material utilization efficiency”). The present invention includes a process for the production of said nickel series rechargeable battery.
2. Related Background Art
In recent years, the global warming of the earth because of the so-called greenhouse effect due to an increase in the content of CO
2
gas in the air has been predicted. For instance, in thermal electric power plants, thermal energy obtained by burning a fossil fuel is being converted into electric energy, and along with burning of such fossil fuel, a large amount of CO
2
gas is being exhausted in the air. Accordingly, in order to suppress this situation, there is a tendency of prohibiting to newly establish a thermal electric power plant. Under these circumstances, so-called load leveling practice has been proposed in order to effectively utilize electric powers generated by power generators in thermal electric power plants or the like, wherein a surplus power unused in the night is stored in rechargeable batteries installed at general houses and the power thus stored is used in the daytime when the demand for power is increased, whereby the power consumption is leveled.
Now, for electric vehicles which do not exhaust any air polluting substances such as CO
2
, NO
x
, hydrocarbons and the like, there is an increased demand for developing a high performance rechargeable battery with a high energy density which can be effectively used therein. Besides, there is also an increased demand for developing a miniature, lightweight, high performance rechargeable battery usable as a power source for portable instruments such as small personal computers, word processors, video cameras, and cellular phones.
In order to comply with these demands, research and development have been vigorously conducting on nickel-series rechargeable batteries in which a nickel hydroxide is used as a cathode active material, specifically nickel-metal hydride rechargeable batteries in which an anode comprising a hydrogen absorption alloy as an anode active material and a cathode a comprising a nickel hydroxide as a cathode active material are arranged through a separator having an alkaline electrolyte solution retained therein nickel-zinc rechargeable batteries in which an anode comprising a zinc material as an anode active material and a cathode comprising a nickel hydroxide as a cathode active material are arranged through a separator having an alkaline electrolyte solution retained therein. And some of these nickel series rechargeable batteries have been putted to practical use.
Incidentally, as the cathode of such nickel series rechargeable battery, a sintered type electrode has been often used. Besides, in order to more increase the battery capacity, there has proposed use of a paste-type electrode comprising a porous metallic body having a high porosity which is filled with a powdery active material of nickel hydroxide kneaded with a solution containing a binder dispersed therein as the cathode of the rechargeable battery. Now, nickel hydroxide as the cathode active material is low in terms of the conductivity and therefore, in the case where the electrode is filled substantially with nickel hydroxide only as above described, it is difficult to attain a sufficient active-material utilization efficiency. In this respect, in order for the cathode to have a sufficient active-material utilization efficiency, there has proposed a method of adding a cobalt metallic powder or a powder of a cobalt compound such as cobalt monoxide to the powdery nickel hydroxide active material upon the formation of the cathode. Here, for the case where cobalt compound is used together with nickel hydroxide in the cathode, there is generally considered such that after the cobalt compound is once dissolved in the alkaline electrolyte solution, it is oxidized upon initially subjecting the rechargeable battery to charging, followed by depositing as a highly conductive cobalt oxyhydroxide on the surface of the nickel hydroxide to form a conductive network over the surface of the nickel hydroxide. However, in the case where the cobalt metallic powder or the cobalt compound powder is added as above described, it is difficult for such cobalt metallic powder or such cobalt compound powder to be uniformly dispersed in the paste, and because of this, it is not ensured that an uniform conductive network is always formed over the surface of the nickel hydroxide.
In this respect, in order to make it possible to form an uniform conductive network over the surface of the to nickel hydroxide, there has proposed a method in which the surface of a nickel hydroxide particulate is covered by a cobalt hydroxide in advance. However, this method is not always effective for the reason that the solubility of the cobalt hydroxide in the alkaline electrolyte solution is inferior and therefore, the cobalt hydroxide is not sufficiently converted into the cobalt oxyhydroxide, where the active-material utilization efficiency is not always sufficient. In addition, the nickel hydroxide is small in terms of the oxygen overvoltage and because of this, especially when charging operation of the nickel-series rechargeable battery is performed under high temperature condition, side reaction of generating oxygen gas is liable to occur, where the charging efficiency is decreased.
In order to eliminate these problems, there have proposed a method in which a cobalt solid solution is incorporated in a nickel hydroxide crystal as the active material of the cathode and a method in which a material capable of increasing oxygen generation potential such as calcium hydroxide or yttrium oxide is added upon the formation of the cathode comprising a nickel hydroxide. However, any of these two methods is not adequate. That is, although the former method has an advantage in that the oxidation potential of the nickel hydroxide is decrease to improve the charging efficiency of the battery, it has a disadvantage in that the discharging voltage of the battery is decreased. For the latter method, it has an advantage in that the charging efficiency of the battery under high temperature condition is improved, but it has a disadvantage in that because not only the calcium hydroxide but also the yttrium hydroxide are inferior in terms of the conductivity, the active-material utilization efficiency of the cathode even under room temperature condition tends to decrease.
Separately, for a nickel series rechargeable battery whose cathode comprises an active material (that is, an active material layer) comprising a nickel hydroxide, there are disadvantages such that the active material layer of the cathode is liable to suffer from a great change in the volume (specifically, the active material layer is liable to repeatedly greatly expand and shrink) upon repeating the charging-and-discharging cycle where when the volume of the active material layer of the cathode is changed, the alkaline electrolyte solution retained in the separator situated between the anode and the cathode is likely to be absorbed by the active material layer of the cathode, resulting in shortening the lifetime of the rechargeable battery. The reason for this is considered as will be described in the following. That is, a
Kawakami Soichiro
Tani Atsushi
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Gulakowski Randy
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