JPH10270039A - Paste nickel hydroxide positive electrode plate for alkaline storage battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a positive electrode plate of which high-efficiency discharging characteristic is improved, by providing it with nickel hydroxide active substance coated with compound mainly consisting of over-bivalent cobalt and at most bivalent cobalt compound. SOLUTION: Amount of compound mainly consisting of over-bivalent cobalt which coats active substance is 1-15 wt.% to the nickel hydroxide. When an alkaline storage battery is composed of such a positive electrode plate, because added at most bivalent cobalt compound solves in alkaline aqueous solution, electrolyte, deposits as cobalt hydroxide on the surface of nickel hydroxide active substances coated with compound mainly consisting of over-bivalent cobalt or in a gap between the active substances, and transforms to oxy-cobalt hydroxide by formation charging or others, electric connection becomes well. Using cobalt monoxide or metallic cobalt instead of cobalt hydroxide, as at most bivalent cobalt, also provides the same effect.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a paste-type nickel hydroxide positive electrode plate for use in an alkaline storage battery whose negative electrode is made of cadmium, a hydrogen storage alloy, zinc or iron.

[0002]

2. Description of the Related Art With the spread of various small portable devices such as portable telephones, video cameras and headphone stereos in recent years, alkaline storage batteries have played an important role as a power source for these devices. Conventionally, as a positive electrode plate of an alkaline storage battery, a sintered positive electrode plate manufactured by impregnating a sintered substrate formed by sintering nickel powder into a perforated steel plate with a nickel hydroxide active material has been used. However, since the porosity of the sintered substrate is about 80%, there is a limit to increasing the capacity of the sintered positive electrode plate.

[0003] Therefore, a paste-type positive electrode plate manufactured by filling an active material paste obtained by mixing powdered nickel hydroxide with various additives on a highly porous three-dimensional porous substrate such as foamed nickel is used. Development is underway and higher capacity has been achieved. However, since a three-dimensional porous body such as foamed nickel has a larger pore diameter than a sintered substrate, there is a problem that the conductivity of the electrode plate is reduced and high-rate discharge performance is reduced.
In order to improve this problem, a method of adding graphite or metallic nickel, and a cobalt compound such as cobalt oxide, cobalt hydroxide or metallic cobalt as a conductive agent, or a method of coating nickel hydroxide with the above conductive agent Has been proposed. A method has also been proposed in which the coated cobalt compound is subjected to an oxidizing treatment to obtain a compound having high conductivity and having more than two valences.

[0004]

The paste type positive electrode plate is
In low-rate discharge, the capacity is higher than that of the sintered electrode plate,
There is a problem that performance is reduced in high-rate discharge. An object of the present invention is to improve the above and provide a paste-type nickel hydroxide positive electrode plate for an alkaline storage battery having improved high-rate discharge characteristics.

[0005]

When the added cobalt compound is divalent or less, the compound is dissolved in an aqueous alkali solution to form a cobalt complex ion, and as cobalt hydroxide, the surface of the nickel hydroxide active material or the active material between the active materials is removed. It is thought that it precipitates in gaps and the like and changes into cobalt oxyhydroxide, which is a stable oxide of higher order by chemical charging and the like, and acts as a conductive agent, thus improving the performance of the nickel hydroxide electrode plate. On the other hand, a cobalt compound having more than two valences has high conductivity by itself, but exists in a stable state due to low solubility in an aqueous alkaline solution.

When nickel hydroxide is coated with a cobalt compound, if the cobalt compound is divalent or less, it dissolves and precipitates, so that the same effect as described above can be obtained. Means that the compound exists in a stable state. In the latter case, it is considered that the active materials only physically contact each other, and therefore, the high-rate discharge performance is inferior.

According to the present invention, there is provided a paste comprising a nickel hydroxide active material coated with a compound mainly composed of cobalt having a valence of more than 2, and a cobalt compound having a valence of 2 or less. The present invention provides a nickel hydroxide positive electrode plate. When an alkaline storage battery is constructed using this positive electrode plate, the added divalent or less cobalt compound is dissolved in an aqueous alkaline solution as an electrolytic solution, and a nickel hydroxide active material coated with a compound mainly composed of more than divalent cobalt is used. It is considered that cobalt hydroxide precipitates as cobalt hydroxide on the surface and in the gaps between the active materials, and becomes cobalt oxyhydroxide by chemical charging or the like.

[0008]

DETAILED DESCRIPTION OF THE INVENTION In the present invention, a paste-type nickel hydroxide for an alkaline storage battery containing a nickel hydroxide active material coated with a compound mainly composed of cobalt having more than two valences and a cobalt compound having two or less valences. A positive electrode plate is used. With this configuration, it is possible to provide an alkaline storage battery having excellent high-rate discharge performance.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below using embodiments.

(Experiment 1) (Example 1) A nickel hydroxide active material was prepared by gradually supplying an alkaline aqueous solution while stirring so that the pH of a 1.5 M nickel sulfate aqueous solution was kept constant. Was precipitated, filtered, washed and dried. Next, purified water is added to the powder to disperse it, and a 10 wt% aqueous solution of cobalt sulfate is added thereto while stirring so as to keep the pH constant, followed by filtration, washing, and drying. A nickel oxide active material was obtained. The coated cobalt hydroxide was bivalent, and its ratio to the nickel hydroxide active material was 5 wt%.

The active material is heat-treated in air at 100 ° C. to oxidize the coated cobalt hydroxide to a state exceeding two valences.

Next, a paste was prepared by dispersing 105 parts by weight of this active material and 5 parts by weight of cobalt hydroxide as a divalent or less cobalt compound in a 0.4 wt% carboxymethylcellulose aqueous solution. A paste-type nickel hydroxide positive electrode plate A according to the present invention was manufactured by filling, drying, and pressing a paste into foamed nickel having a porosity of 95% (trade name: Celmet, manufactured by Sumitomo Electric Industries, Ltd.).

This positive electrode plate A and a known sintered cadmium negative electrode plate having a capacity sufficiently larger than that of the positive electrode and partially charged by a chemical conversion treatment are spirally wound via a hydrophilic polypropylene separator. , 7 as electrolyte
Sealed nickel of KR-AA size with a nominal capacity of 1000 mAh using an aqueous solution mainly composed of M potassium hydroxide
Cadmium battery A (hereinafter, battery A of the present invention) was manufactured.

Comparative Example 1 A method similar to that of Example 1 except that the nickel hydroxide active material coated with cobalt hydroxide prepared by the method described in Example 1 was used without performing an oxidation treatment. To produce a positive electrode plate B, and a comparative battery B was produced.

(Comparative Example 2) A nickel hydroxide active material coated with a cobalt hydroxide having a valence of more than 2 by performing the oxidation treatment described in the above Example 1 was prepared by dispersing it in a 0.4 wt% carboxymethylcellulose aqueous solution. Except for using the paste thus obtained, a positive electrode plate C consisting only of the active material coated with cobalt hydroxide having more than two valencies was produced in the same manner as in Example 1, and a comparative battery C was produced.

The above battery was charged at 25 ° C. to 0.1 Cm
A (100mA), first charge for 15 hours, then 0.2C
The battery was discharged at 1 mA at 200 mA. Furthermore, 1C
Charged for 1.2 hours at 1 mA (1000 mA)
(1000 mA) to 1 V
Cycle. Next, after charging under the same conditions, discharging was performed at 3 CA (3000 mA). FIG. 1 shows a comparison of the discharge characteristics at this time.

FIG. 1 shows that the battery A of the present invention using a nickel hydroxide active material coated with cobalt hydroxide having a valence of more than 2 and a positive electrode plate A containing cobalt hydroxide which is a cobalt compound having a valence of 2 or less. Comparative battery B using nickel hydroxide active material coated with divalent or less cobalt hydroxide and positive electrode plate B containing divalent or less cobalt hydroxide, and water coated with more than divalent cobalt hydroxide Compared with a comparative battery C using a positive electrode plate C made of only a nickel oxide active material,
It can be seen that the polarization during discharge is small and the discharge capacity is large.

This is because, in the battery A of the present invention, the added cobalt hydroxide, which is a cobalt compound having a valence of 2 or less, is dissolved in the alkaline electrolyte and precipitated as cobalt hydroxide on the surface of the active material and the gap between the active materials. It is considered that, because it changed to cobalt oxyhydroxide and acted as a conductive agent, the electrical connection became better than the comparative battery C.

In the comparative battery B using the nickel hydroxide active material coated with divalent cobalt hydroxide, the effect was small because the degree of dissolution or precipitation of the added or coated cobalt hydroxide was within the electrode plate. In the case where cobalt hydroxide is oxidized to cobalt oxyhydroxide during chemical formation charging, there is no cobalt hydroxide having more than two valences having high conductivity unlike the battery A of the present invention. This is probably due to the poor condition.

(Experiment 2) In order to limit the amount of the cobalt compound having a valence of more than 2 to coat the nickel hydroxide and the amount of the cobalt compound having a valence of 2 or less to be added, each amount was determined in accordance with Example 1. Various kinds of electrode plates were manufactured by changing, and the same test as described above was performed. The test results are shown in Table 1 with the amount of nickel hydroxide being 100 (wt%).

[0021]

[Table 1] From Table 1, it can be seen that when the amount of the coated cobalt compound having more than two valences is less than 1 wt% and when it is 15 wt% or more, the discharge capacity is small, and the appropriate value is 1 to 14 wt%. Also, when the amount of the added divalent or less cobalt compound is less than 1 wt% or more than 15 wt%, the discharge capacity is small, and the appropriate value is 1 to 14 wt%.

The reason for the small discharge capacity is considered that the effect of improving the conductivity of the active material is small when the amount of the coated cobalt hydroxide having a valence of more than 2 is less than 1 wt%. If the amount of the added divalent or less cobalt hydroxide is less than 1 wt%, it is considered that the effect of improving the conductivity between the active material and the substrate is small. On the other hand, when the amount of the coated cobalt hydroxide having a valence of more than 2 or the added amount of the cobalt hydroxide having a valence of 2 or less is 15 wt% or more, it is considered that the occupied volume of the nickel hydroxide active material was reduced.

In the positive electrode plate according to the present invention shown in the examples, cobalt hydroxide was used as the divalent or lower valent cobalt compound. However, the same effect can be obtained by using cobalt monoxide, cobalt suboxide or metallic cobalt. Obtained.
The method of oxidizing the coated cobalt hydroxide is not limited to the method described in the present embodiment, and an oxidizing agent such as potassium permanganate or a known method such as anodic oxidation can be used. Further, the present invention does not hinder a means for coprecipitating cobalt, zinc, cadmium and the like in nickel hydroxide to improve various performances of the positive electrode plate.

Needless to say, the effect of the paste-type positive electrode plate according to the present invention is not limited to a nickel-cadmium battery, but is also effective for an alkaline storage battery using a hydrogen storage alloy, zinc, iron or the like for the negative electrode. .

[0025]

The paste-type nickel hydroxide positive electrode plate for an alkaline storage battery according to the present invention provides an alkaline storage battery excellent in high-rate discharge performance, and its industrial value is extremely large.

[Brief description of the drawings]

FIG. 1 is a diagram showing a comparison of discharge characteristics of each battery.

Claims (3)

[Claims] 1. A paste formula for an alkaline storage battery, comprising a nickel hydroxide active material coated with a compound mainly composed of cobalt having a valence of more than 2 and a compound mainly composed of cobalt having a valence of 2 or less. Nickel hydroxide positive electrode plate. 2. The coated nickel hydroxide active material 2
The paste-type nickel hydroxide positive electrode plate for an alkaline storage battery according to claim 1, wherein the amount of the compound mainly composed of cobalt having a valency is 1 to 15 wt% based on nickel hydroxide. 3. The paste type water for an alkaline storage battery according to claim 1, wherein the amount of the compound mainly composed of divalent or less cobalt is 1 to 15% by weight based on nickel hydroxide. Nickel oxide positive plate.