JPH11144726A - Non-sintered type nickel hydroxide electrode for alkaline storage battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the reduction in discharge capacity, accompanied by the reduction of utilization factor by adding a compound composed mainly of a cobalt having a valence exceeding 2 to an active material powder, composed mainly of nickel hydroxide and nickel oxyhydroxide. SOLUTION: A cobalt compound powder to be added to a nickel hydroxide electrode is a highly conductive high-order cobalt compound having a valence of cobalt exceeding 2. Therefore, high conductivity can be kept, without causing uneven presence of the cobalt compound by its oxidation by the nickel oxyhydroxide as a cobalt compound having a valence of 2 or less. Thus, a high active material utilization factor can be shown. Since it is required to prevent the oxidation of the cobalt compound by the nickel oxyhydroxide in order to make this effect more effective, the valence of the cobalt compound is preferably 2.5 or more. Thus, the capacity of the battery can be increased more effectively.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to increasing the capacity of an alkaline storage battery using a non-sintered nickel hydroxide electrode.

[0002]

2. Description of the Related Art A nickel hydroxide electrode using nickel hydroxide as an active material is used as a positive electrode of an alkaline storage battery such as a nickel-cadmium storage battery or a nickel-metal hydride storage battery. These alkaline storage batteries are used as a power source for portable electronic devices, and a high capacity of these alkaline storage batteries is required as a means for improving their functions. Therefore, it is essential to improve the performance of nickel hydroxide electrodes.

Conventionally, as a nickel hydroxide electrode, a sintered type electrode manufactured by impregnating a nickel powder active material on a substrate obtained by sintering nickel powder on a porous punching metal. Has been widely used. But,
In the sintered type electrode plate, the porosity of the substrate is as small as approximately 80%,
Since it is difficult to fill a large amount of active material, it is disadvantageous for increasing the energy density of the nickel hydroxide electrode.

On the other hand, a non-sintered nickel hydroxide electrode using a foamed nickel or fibrous nickel mat for the substrate has a high porosity of 95% or more, which is higher than that of the sintered electrode plate. This is advantageous for increasing the energy density of the nickel hydroxide electrode. Therefore, recent studies on increasing the capacity of alkaline storage batteries have been conducted mainly using non-sintered electrodes. Since the non-sintered nickel hydroxide electrode has low conductivity of the substrate, it is necessary to add a cobalt compound such as cobalt hydroxide or cobalt monoxide as a conductive agent. This added cobalt compound is electrochemically oxidized at the initial charge of formation, converted to highly conductive cobalt oxyhydroxide, and is considered to act as an effective conductive agent in the nickel hydroxide electrode. .

[0005] Nickel hydroxide, which is a positive electrode active material of an alkaline storage battery, is oxidized to nickel oxyhydroxide by charging and reduced to nickel hydroxide by discharging. This nickel oxyhydroxide is a substance having higher conductivity than nickel hydroxide. Therefore, Japanese Patent Application Laid-Open No. 2-262
As disclosed in Japanese Patent Publication No. 245, it is possible to increase the conductivity of the positive electrode by uniformly adding nickel oxyhydroxide powder in advance at the time of manufacturing the nickel hydroxide electrode.

However, if the amount of nickel oxyhydroxide added exceeds 20 wt% of the entire active material, it is expected that the capacity-limiting electrode during discharge of the alkaline storage battery will be the negative electrode. In order to sufficiently obtain the effect of adding nickel oxyhydroxide, it is desirable that the amount of nickel oxyhydroxide added is large. For these reasons, it is preferable that the addition amount of nickel oxyhydroxide is about 10 to 20 wt%.

However, when a cobalt compound required for a non-sintered nickel hydroxide electrode is added to a nickel hydroxide electrode containing nickel oxyhydroxide, the valence of cobalt such as cobalt hydroxide or cobalt monoxide is increased. However, when a compound having a valency of 2 or less is added, there is a problem that the discharge capacity decreases due to a decrease in the utilization rate of the active material. This is because part of the cobalt compound having a valence of 2 or less is oxidized by nickel oxyhydroxide to form a higher-order cobalt compound, so that the cobalt compound tends to be unevenly distributed. Is estimated to be smaller.

[0008]

SUMMARY OF THE INVENTION The present invention relates to a non-sintered nickel hydroxide electrode in which nickel oxyhydroxide powder is added, in which the discharge capacity is not reduced due to a decrease in utilization. The purpose is to provide.

[0009]

According to the present invention, there is provided a non-sintered nickel hydroxide electrode for an alkaline storage battery, wherein the active material comprises a powder mainly composed of nickel hydroxide and a nickel oxyhydroxide. Characterized by comprising these active material powders and a compound powder mainly composed of cobalt having a valence of more than 2 valences.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The cobalt compound powder to be added to the nickel hydroxide electrode of the present invention is a high-order cobalt compound having high conductivity in which the valence of cobalt exceeds two.
Therefore, as in the case of a divalent or lower valent cobalt compound, high conductivity can be maintained without being oxidized by nickel oxyhydroxide and uneven distribution of the cobalt compound. In order to make this effect more effective, it is necessary to prevent oxidation of the cobalt compound by nickel oxyhydroxide. Therefore, the valence of the cobalt compound is preferably 2.5 or more.

[0011]

EXAMPLES The nickel hydroxide electrode according to the present invention will be described in detail with reference to examples and comparative examples.

(Example) As shown in JP-A-2-262245, according to the following chemical reaction formula (1), S.I. G. FIG. 1.2
Nickel hydroxide powder and potassium peroxodisulfate powder in a 5 (20 ° C.) aqueous sodium hydroxide solution at a molar ratio of 2.
It was dispersed at a ratio of 4: 1, and stirred at room temperature for 10 hours. The black powder obtained by filtering this dispersion is washed with the pH of the washing solution.
Was washed and dried with purified water until the value became 7. Nickel oxyhydroxide powder was obtained.

2Ni (OH) ₂ + S ₂ O ₈ ²⁻ + 2OH ⁻ → 2NiOOH + 2SO ₄ ²⁻ + 2H ₂ O (1) The average valence of the nickel oxyhydroxide thus obtained is determined by redox titration. It was confirmed to show 98 valence.

Next, as a cobalt compound having more than two valences, cobalt hydroxide powder was added to S.I. G. FIG. 1.25 (20 ° C)
Heat treatment, washing and drying were performed at 80 ° C. in an aqueous sodium hydroxide solution to produce a highly conductive trivalent cobalt compound. 10 parts by weight of this powder and the nickel oxyhydroxide powder 1
5 parts by weight, 85 parts by weight of nickel hydroxide powder, and 2 parts by weight of carboxymethylcellulose powder were added to purified water, and a slurry sample produced was impregnated and pressed into a foamed nickel substrate, dried, and dried according to the present invention. A nickel hydroxide electrode A was obtained.

The negative electrode was manufactured by applying a slurry sample containing a known AB5 type hydrogen storage alloy as a main component on a punching metal, drying and pressing.

A battery can in which an element is formed using the three positive electrode plates and the four negative electrode plates manufactured as described above and a polyolefin separator provided with hydrophilicity, and into which an electrolyte mainly containing an aqueous solution of potassium hydroxide is injected. The battery A of the present invention was obtained by welding the battery can and the cover part containing the safety valve.

Comparative Example A nickel hydroxide electrode B was manufactured in the same manner as the nickel hydroxide electrode A of the example except that 10 parts by weight of cobalt hydroxide powder was used, and a comparative battery B was obtained.

In these batteries, the theoretical capacity of the positive electrode is 1000 mAh.

The above battery was subjected to 12 mA at room temperature at 100 mA.
After charging for 10 hours, the charge / discharge cycle of discharging to 0.8 V at 100 mA was repeated 10 times to sufficiently activate the hydrogen storage alloy negative electrode, and then the discharge capacity was measured under the following conditions.

Charge: 120% at 200 mA (6 hours) Discharge: up to 0.8 V at 200 mA Temperature: 25 ° C. The test results are shown in FIG. The discharge capacity of the comparative battery B containing the nickel hydroxide powder, the nickel oxyhydroxide powder and the cobalt hydroxide powder was as small as about 780 mAh. The discharge capacity of the battery A of the present invention containing the cobalt compound powder showed a large value of about 980 mAh.
The reason why the discharge capacity of the comparative battery B is small is that part of the cobalt hydroxide powder, which is a divalent cobalt compound, is oxidized by nickel oxyhydroxide and the cobalt compound is unevenly distributed, and the conductive network of the cobalt oxyhydroxide is It was not formed sufficiently. On the other hand, in the battery A of the present invention, since the cobalt compound is a higher-order cobalt compound having more than two valencies, it is considered that high conductivity can be maintained without being oxidized by nickel oxyhydroxide.

Even if a small amount of a hydroxide such as zinc, cobalt or cadmium is contained in the nickel hydroxide powder or the nickel oxyhydroxide powder, it does not deteriorate the characteristics of the electrode of the present invention. Absent. Also, oxidation of nickel hydroxide powder for the production of nickel oxyhydroxide powder,
The method for obtaining a cobalt compound powder having more than two valencies may be any of an electrochemical method and a chemical method.

[0022]

As described in detail above, the use of nickel oxyhydroxide powder, nickel hydroxide powder, and a high-order cobalt compound powder having more than two valences enables oxidation of a cobalt compound by nickel oxyhydroxide. Therefore, it is possible to prevent the discharge capacity from decreasing. This effect makes it possible to increase the capacity of the alkaline storage battery by adding nickel oxyhydroxide powder to the nickel hydroxide electrode, which is more effective.

[Brief description of the drawings]

FIG. 1 shows a comparison of discharge characteristics of various batteries.

Claims (1)

[Claims] 1. An active material comprising a powder mainly composed of nickel hydroxide and a powder mainly composed of nickel oxyhydroxide, wherein the active material powder and a compound powder mainly composed of cobalt having a valence of more than 2 valences are used. A non-sintered nickel hydroxide electrode for an alkaline storage battery, comprising: