JPS5814026B2 - iron alkaline storage battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an iron alkaline storage battery, typified by a nickel-iron battery, and aims to improve charging and discharging characteristics.

More specifically, it is characterized by adding a small amount of tellurium together with potassium sulfide or sodium sulfide to the alkaline electrolyte in order to significantly improve the self-discharge characteristics, which have been a drawback of iron electrodes.

Batteries using iron electrodes have long been known as engine batteries, and research is also being conducted into iron-air batteries, iron-iron silver oxide batteries, etc.

However, while iron plates have advantages such as higher capacity and lower cost than cadmium electrodes, they tend to have poorer charge-discharge characteristics.

Among charge-discharge characteristics, discharge characteristics such as discharge utilization rate and discharge capacity have been significantly improved by improvements in iron electrode materials and electrode manufacturing methods.On the other hand, self-discharge characteristics have hardly been improved by these studies. The current situation is that it cannot be improved.

As a countermeasure to this problem, since the small hydrogen overvoltage of the iron electrode is thought to be the main cause, attempts have been made to use metals with high hydrogen overvoltage, such as mercury, cadmium, lead, or antimony, as additives.

It is also known to coat a part of the active iron electrode, which serves as a hydrogen generation point, with an amine-based adsorptive organic substance.

However, although the effects of these additives have been recognized to some extent, they have not yet achieved a definitive effect.

Therefore, in order to widely put into practical use iron electrodes that are inexpensive, have high capacity, and can be expected to have a long life, it is necessary to explore new additives.

The present invention aims to meet this demand by adding tellurium to the electrolytic solution together with potassium sulfide or sodium sulfide.

When tellurium is added, the effect changes greatly depending on the amount added, and the optimum amount is 0.005 to 0.03 mol/l.
It is.

The reason why the addition of tellurium and potassium sulfide or soda sulfide produces an effect is not clear, but tellurium is adsorbed or deposited on the surface of the iron electrode activated by sulfur ions.
It is presumed that both of them work synergistically to improve the self-discharge characteristics.

As will be shown later, the above effects cannot be achieved with only sulfur ions or tellurium alone.

Tellurium usually becomes a tellurite ion when tellurium dioxide Te02 is dissolved in an alkaline electrolyte.

Therefore, it can be assumed that these ions are adsorbed on the surface of the iron electrode or electrodeposited in the form of metallic tellurium during charging, thereby improving the characteristics of the iron electrode such as self-discharge.

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

Figure 1 shows a nickel-iron storage battery, and 1 in the figure is a sintered iron electrode made by keeping electrolytic iron powder in a hydrogen stream at 850°C for about 30 minutes.

The size is 50 x 60 mm, the thickness is about 1.0 mm,
The porosity is approximately 62%, and the discharge capacity after formation is approximately 2Ah.
/ piece.

2 is an iron terminal, 3 is a nickel electrode, and 4 is its terminal.

The thickness of the sintered nickel electrode 3 is about 1.2 mu1, and the size is the same as that of the iron electrode, and the discharge capacity is about 1.2 mu1. IAh/piece.

The electrode configuration of this battery consists of four iron electrodes and five nickel electrodes arranged alternately with separators in between.

In addition, 5 is added to a 25% weight potassium aqueous solution at 5.0 g/l.
of potassium sulfide and 0.01 mol/l (approximately 1.6 g/l) of T
An electrolytic solution in which eO2 is dissolved, 6 a separator made of nylon fabric, and 7 a battery case made of polyvinyl chloride.

The battery manufactured with the above configuration is referred to as A. For comparison, battery B is the same as battery A except that no potassium sulfide is added to the electrolyte, and battery A is the same as battery A except that no tellurium is added to the electrolyte. An identical battery C was manufactured.

These batteries were chemically charged at 25° C. at a rate of 5 hours for 7 hours, and the discharge capacity of the batteries was confirmed.

Naturally, the discharge capacity follows the nickel polar rule, and 5
The hourly rate was approximately 5.5 Ah.

Although the iron electrode capacity could not be measured, it is thought to be about 8 Ah.

Self-discharge of these batteries at 25°C was investigated.

The results are shown in FIG. 2, where curves A, B, and C are for battery A. The results of B and C are shown.

From this figure, if both tellurium and potassium sulfide according to the present invention are used, the effect is even greater than when they are used alone, and even after 5 months, approximately 73% of the capacity is retained, compared to less than 20% when used alone. , the difference is clear.

Note that since the self-discharge of the nickel electrode is relatively small, it is clear that these results relate to the self-discharge of the iron electrode.

Next, we investigated the effect of additive concentration.

Regarding potassium sulfide or soda sulfide, the influence of self-discharge due to concentration was small, and the presence of even a small amount did not pose a particular problem.

On the other hand, for tellurium, there is an optimum concentration range, and the results are shown in FIG.

This result is experimental data for a battery that has the same structure as the battery described above but differs only in the concentration of the additive.

As is clear from this figure, the optimal range of tellurium concentration is
0005 to 0.03 mol/l, and outside this range the effect was extremely reduced.

The reason why self-discharge increases when there is too much tellurium is not clear, but it can be assumed that a local battery is formed between dissimilar metals due to a large amount of tellurium being deposited on the surface of the iron electrode.

Even if the charging/discharging conditions and self-discharge measurement conditions shown in the above examples were changed, the effects of these additives were clearly observed.

Furthermore, even when an air electrode, a silver oxide electrode, or the like was used instead of a nickel electrode for the positive electrode, the effects of these additives on the iron electrode were the same.

Furthermore, in this example, tellurium was replaced with tellurium dioxide (TeO2
), but telluric acid (H2TeO4・2H20
), tellurium tetrachloride (TeCl4), etc. may be added.

As described above, according to the present invention, self-discharge of iron batteries can be significantly reduced by dissolving tellurium together with potassium sulfide or sodium sulfide in an electrolytic solution.

[Brief explanation of the drawing]

Figure 1 is a vertical cross-sectional view of a Nickel iron battery showing an example of the present invention, Figure 2 is a diagram showing changes in remaining capacity when batteries using various electrolytes are left unused, and Figure 3 is a diagram showing tellurium in the electrolyte. The relationship between the concentration and the remaining capacity after 5 months of storage is shown. 1...Negative electrode, 3...Positive electrode, 5...
... Electrolyte.

Claims (1)

[Scope of Claims] 1. An iron alkaline storage battery comprising a negative electrode and a positive electrode using iron as an active material, and an alkaline electrolyte, the electrolyte containing tellurium and potassium sulfide or soda sulfide. 2 The amount of tellurium added is 0.005 to 0.03 mol/l
An iron-alkaline storage battery according to claim 1.