JPH0555980B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a paste-type cadmium negative electrode used in a sealed alkaline storage battery.

Conventional technology In general, in sealed alkaline storage batteries, in order to prevent the internal pressure from increasing due to gas generation due to water electrolysis during overcharging, (1) the oxygen gas generated from the positive electrode is replaced by the charging product of the negative electrode. (2) By making the electrochemical capacity of the active material filled in the negative electrode larger than the electrochemical capacity of the active material filled in the positive electrode, hydrogen gas generation from the negative electrode is prevented. A method is being taken. However, even when these methods are used, the internal pressure level during overcharging is high, so there is a need for a negative electrode that has characteristics that can further prevent the internal pressure of the battery from increasing.

Problems to be solved by the invention In order to solve these problems, the invention
As seen in Publication No. 81765, it has been proposed to form a carbon powder layer on the electrode surface, but such negative electrodes can increase oxygen gas absorption, but do not have water that can accept charge. It was not possible to suppress the increase in internal pressure due to hydrogen gas when no cadmium oxide remained in the electrode plate.

The present invention solves the above-mentioned conventional drawbacks,
The purpose of the present invention is to provide a paste-type cadmium negative electrode that exhibits extremely little increase in internal pressure due to hydrogen gas even under severe charging conditions.

Means for Solving the Problems In order to solve the above problems, the paste-type cadmium negative electrode of the present invention forms a layer consisting of a carrier powder supporting a catalyst and a binder on the electrode surface, and then A porous fluororesin membrane is formed on the surface.

Function This type of paste-type cadmium negative electrode has a layer made of a binder and a carrier powder supporting a catalyst formed on the electrode surface, and a porous film of fluororesin is further formed on the surface of this layer. , it becomes possible to electrochemically absorb hydrogen gas generated during overcharging, and hydrogen gas can prevent internal pressure from increasing.

Example The present invention will be explained in detail with reference to Examples below.

A solution of polyvinyl alcohol in ethylene glycol is added to cadmium oxide powder with an average particle size of approximately 1μ, and the mixture is kneaded to form a paste. This paste was applied to a conductive support, a nickel-plated perforated steel plate with a thickness of 0.1 mm, and dried at approximately 140°C for 30 minutes.
An electrode with a thickness of about 0.5 mm was obtained.

Furthermore, artificial graphite powder is added to a solution of palladium chloride dissolved in hydrochloric acid, and the mixture is kneaded to cause palladium to be adsorbed onto the graphite. An aqueous sodium hydroxide solution and formalin were added thereto to reduce the adsorbed palladium, followed by washing with water and drying to obtain graphite powder adsorbing about 1% by weight of palladium.

The electrode was immersed for about 10 seconds in a solution in which 30% by weight of this graphite powder and 5% by weight of polyvinyl alcohol were dispersed in pure water, and then dried at 80°C.
A layer was formed on the electrode surface. Next, this electrode was charged to about 40% of its theoretical capacity in an alkaline solution, washed with water, and dried to form a porous fluororesin membrane.
For example, it was immersed in a 3% by weight fluororesin dispersion liquid and dried to obtain a paste-type cadmium negative electrode. Let this negative electrode be a.

On the other hand, a cadmium negative electrode of a comparative example having the same structure except that no layer was formed on the surface by the above method was prepared. Let this be b.

Furthermore, using a solution containing 30% by weight of artificial graphite powder without adsorbing palladium and 5% by weight of polyvinyl alcohol, a comparative example of cadmium negative electrode C was obtained in which a layer was similarly formed on the surface. .

A sealed storage battery was prototyped by combining the three types of cadmium negative electrodes mentioned above with a sintered nickel positive electrode.
Internal pressure tests were conducted during overcharging and during charging after battery storage. The internal pressure test during overcharging was conducted under the following conditions. 15 at a current equivalent to 0.1C at 20℃
After charging for 2 hours and leaving at 20℃ for 2 hours, at 0℃
The battery was charged for 2 hours at a current equivalent to 1.5C and discharged at a current equivalent to 1.5C at 0°C. At this time, the charging start time at 0° C. was set as 0, and the change in battery internal pressure over time was measured. Furthermore, an internal pressure test during charging after electronic storage was conducted as follows. Charge the battery at 20℃ for 10 hours with a current equivalent to 0.1C, leave it at 45℃ for one month, and then charge the battery at 20℃ with a current equivalent to 0.2C.
The battery was charged for 2 hours at an equivalent current and discharged at a current equivalent to 0.2C at 20°C. At this time, the charging start time at 0.2C was set as 0, and the change in battery internal pressure over time was measured.

FIG. 1 shows the relationship between battery internal pressure and time in an internal pressure test during overcharging. A shows a battery using the negative electrode of the present invention, and b and c show batteries using negative electrodes for comparison. Further, the equilibrium pressure h after discharge indicates the residual hydrogen pressure within the battery. As is clear from this result,
Negative electrode a with a layer containing graphite powder formed on the electrode surface
Batteries a and c using negative electrodes a and c have a significantly reduced internal pressure compared to a battery using negative electrode b in which no layer is particularly formed on the electrode surface. This is thought to be because the formation of a conductive layer on the electrode surface facilitated the generation of metal cadmium, which is involved in gas absorption, near the surface. Further, in battery a using negative electrode a in which graphite powder on which palladium is adsorbed is used for the surface layer, the hydrogen residual pressure after discharge is zero. This is due to the action of a catalyst.
This is thought to be because the generated hydrogen gas is absorbed electrochemically. Furthermore, when comparing the internal pressure curve of battery a with the internal pressure curve of battery using negative electrode c using graphite powder that does not adsorb palladium, they have almost the same shape, so the action of the catalyst mainly affects hydrogen gas absorption. It is thought that it is being carried out.

FIG. 2 shows the relationship between battery internal pressure and time in an internal pressure test during charging after battery storage. As is clear from the figure, results similar to those obtained in the internal pressure test during overcharging were obtained in this test as well. By overcharging, the cadmium hydroxide in the negative electrode changes to metallic cadmium, and when there is no longer any cadmium hydroxide that can accept charging, hydrogen gas is generated if charging is continued. Also,
When a battery is stored, γ-type cadmium hydroxide, which easily accepts charge, changes to β-type cadmium hydroxide, which does not easily accept charge, so hydrogen gas is generated when the battery is charged. In this embodiment, hydrogen gas can be electrochemically absorbed in any case. Since a porous film of fluororesin is formed on the surface of the layer, the gas phase for introducing hydrogen gas is easily and reliably maintained, promoting hydrogen gas to reach the catalyst, and eliminating hydrogen gas by the catalyst. can be carried out more smoothly.

In addition, although palladium was used as the catalyst in the examples,
A similar effect can be obtained by using platinum. Regarding the layer thickness, it is technically difficult to reduce it to 0.5μ or less, and if the layer becomes thicker than 20μ, actual charging and discharging becomes impossible, so the layer thickness should be 0.5μ or less.
It can be said that ~20μ is appropriate. In addition, although polyvinyl alcohol was used as a binder in the examples,
Similar effects can be obtained by using other water-soluble binders such as methylcellulose or water-insoluble binders such as fluororesin.

Effects of the Invention As described above, according to the present invention, an increase in internal pressure of an alkaline storage battery can be suppressed even under severe charging conditions.

[Brief explanation of the drawing]

FIGS. 1 and 2 are diagrams showing changes over time in the internal pressure of a nickel-cadmium storage battery using the negative electrode of the present invention.

Claims (1)

[Claims] 1. A paste type, characterized in that a layer consisting of a carrier powder supporting a catalyst and a binder is formed on the surface of an electrode, and a porous film of fluororesin is further formed on the surface of this layer. Cadmium negative electrode. 2. The paste-type cadmium negative electrode according to claim 1, wherein the catalyst is palladium or platinum. 3. The paste-type cadmium negative electrode according to claim 1 or 2, wherein the carrier powder is carbon powder. 4. The paste-type cadmium negative electrode according to claim 1, wherein the layer has a thickness of 0.5 to 20μ.