Enclosed alkali storage battery

Details Enclosed alkali storage battery Enclosed alkali storage battery

1999-06-30

2001-05-22

Weiner, Laura (Department: 1745)

Chemistry: electrical current producing apparatus, product, and

Current producing cell, elements, subcombinations and...

Electrode

C429S224000, C429S229000, C429S231000, C429S163000

Reexamination Certificate

active

06235428

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a sealed alkaline storage battery including a positive electrode active material and a negative electrode active material packed in total in a battery can at 75% by volume or more of the content volume of the battery can. More particularly, it relates to improvement of a positive electrode active material for the purpose of providing a highly reliable sealed alkaline storage battery from which an electrolyte hardly leaks for a long period of charge-discharge cycles.
BACKGROUND ART
Manganese dioxide has been proposed as a positive electrode active material for a sealed alkaline storage battery using zinc as a negative electrode active material (Japanese Patent Publication No. 45-3570). Also, a mixture of nickel oxide and manganese dioxide has been proposed as a positive electrode active material for an alkaline primary battery using zinc as a negative electrode active material (Japanese Laid-Open Patent Publication No. 49-114741).
However, manganese dioxide is poor in reversibility in a charge-discharge reaction and is difficult to return to manganese dioxide by charge after discharge. Therefore, the utilization of the active material is rapidly lowered through repeated charge-discharge cycles, resulting in rapidly decreasing the discharge capacity. Furthermore, the oxygen evolution potential of manganese dioxide is so low that the pressure within the battery is increased due to an oxygen gas generated through decomposition of water on the positive electrode during charge. As a result, the adhesion in a connecting portion of a battery housing member is degraded, so that the electrolyte can easily leak.
On the other hand, when the mixture of nickel oxide and manganese dioxide is used in a storage battery (secondary battery) that is repeatedly charged and discharged, the oxygen evolution potential of the mixture is so low that the pressure within the battery can be easily increased during charge and the electrolyte can easily leak similarly to the battery using manganese dioxide. Furthermore, manganese dioxide included in the mixture is poor in reversibility in a charge-discharge reaction, and hence, the utilization of the active material is rapidly lowered through repeated charge-discharge cycles, resulting in rapidly decreasing the discharge capacity.
In this manner, both of the positive electrode active materials are too disadvantageous to be used as a positive electrode active material for a sealed alkaline storage battery. The increase of the pressure within a battery during charge and the resultant leakage of the electrolyte are particularly significant in a sealed alkaline storage battery including an active material in a large amount.
Accordingly, an object of the invention is providing a highly reliable sealed alkaline storage battery including an active material in a large amount but hardly suffering electrolyte leakage for a long period of charge-discharge cycles.
Another object of the invention is providing a sealed alkaline storage battery that can keep high utilization of an active material not only in initial stages of charge-discharge cycles but also for a long period of time.
DISCLOSURE OF INVENTION
The sealed alkaline storage battery (hereinafter referred to as the “first battery”) according to claim
1
(first invention) comprises a negative electrode of a zinc electrode, a cadmium electrode or a hydrogenated hydrogen-absorbing alloy electrode; and a positive electrode active material and a negative electrode active material packed in total in a battery can at 75% by volume or more of a content volume of the battery can, and the positive electrode active material includes 60 through 100 wt % of nickel oxyhydroxide including Mn as a solid-solution element and having a &ggr; ratio defined as follows of 65 through 100%, and 40 through 0 wt % of &agr;-Ni(OH)
2
:
&ggr; ratio (%)={
S
1
/(
S
1
+
S
2
)}×100
in which S
1
indicates a peak area in a lattice plane (003) in an X-ray diffraction pattern of the nickel oxyhydroxide including Mn as a solid-solution element; and S
2
indicates a peak area in a lattice plane (001) in the X-ray diffraction pattern of the nickel oxyhydroxide including Mn as a solid-solution element.
The peak area S
1
in the lattice plane (003) in the above-described formula corresponds to the amount of &ggr;-nickel oxyhydroxide included in the nickel oxyhydroxide, and the peak area S
2
in the lattice plane (001) in the formula corresponds to the amount of &bgr;-nickel oxyhydroxide included in the nickel oxyhydroxide. Accordingly, the &ggr; ratio corresponds to the proportion (%) of &ggr;-nickel oxyhydroxide in the nickel oxyhydroxide.
The first battery uses the positive electrode active material including 65 through 100 wt % of nickel oxyhydroxide including Mn as a solid-solution element and having a &ggr; ratio of 65 through 100%, and 40 through 0 wt % of &agr;-Ni(OH)
2
. When the proportion of the nickel oxyhydroxide including Mn as a solid-solution element is smaller than 60 wt %, namely, when the proportion of &agr;-Ni(OH)
2
exceeds 40 wt %, the oxygen overvoltage of the positive electrode becomes too low to obtain a sealed alkaline storage battery hardly suffering electrolyte leakage for a long period of charge-discharge cycles. Also, when the &ggr; ratio is smaller than 65% and a large amount of &bgr;-nickel oxyhydroxide is included, the oxygen overvoltage of the positive electrode is so low that an oxygen gas can be easily generated. The &ggr; ratio is preferably 90 through 100%.
The nickel oxyhydroxide including Mn as a solid-solution element can be obtained by oxidizing nickel hydroxide including Mn as a solid-solution element with an oxidizing agent. Examples of the oxidizing agent are sodium hypochlorite, potassium permanganate and potassium persulfate. A desired &ggr; ratio can be attained by increasing/decreasing the amount of the oxidizing agent to be added. When a larger amount of the oxidizing agent is added, a higher &ggr; ratio is attained.
The nickel oxyhydroxide including Mn as a solid-solution element preferably has a Mn ratio defined as follows of 5 through 50%:
Mn ratio (%)={
M
/(
M+N
)}×100
wherein M indicates the number of Mn atoms included in the nickel oxyhydroxide including Mn as a solid-solution element; and N indicates the number of Ni atoms included in the nickel oxyhydroxide including Mn as a solid-solution element.
When the Mn ratio is lower than 5%, the oxygen overvoltage (oxygen evolution potential—charge potential) cannot be sufficiently increased by adding Mn as a solid-solution element to nickel oxyhydroxide, and hence, an oxygen gas can be easily generated on the positive electrode. On the other hand, when the Mn ratio is higher than 50%, Mn cannot be completely dissolved as a solid-solution element in nickel oxyhydroxide, and hence, a generated free Mn oxide obstructs the discharge.
The Mn ratio is equal to the proportion (%) of the number of Mn atoms included in the nickel hydroxide including Mn as a solid-solution element to the total number of Mn atoms and Ni atoms. Accordingly, nickel oxyhydroxide having a desired Mn ratio can be obtained by adjusting the amounts of a Mn material (such as manganese sulfate) and a Ni material (such as nickel sulfate) to be mixed for preparing nickel hydroxide including Mn as a solid-solution element.
The first invention is applied to a sealed alkaline storage battery including the active materials packed in total in the battery can at 75% by volume or more of the content volume of the battery can for the following reason: Particularly in a sealed alkaline storage battery including a large amount of active materials packed in a battery can, the pressure within the battery is easily increased, and the electrolyte can easily leak during repeated charge-discharge cycles. The increase of the pressure within the battery can be remarkably suppressed by using the positive electrode active material having a high oxygen overvoltage according to the first invention.
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