JP2000277107A - Negative electrode active material for alkaline storage battery and alkaline storage battery used therewith - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a negative electrode active material for an alkaline storage battery of the reduced abnormal discharge generation when intermittent discharge as maintaining the amount of a hydrogen gas generated from a zinc when touched to an electrolyte at a present level or under, and to provide a battery used therewith. SOLUTION: By utilizing a zinc powder alloyed with 10 ppm or under of Al, 10-1000 ppm of Bi and 100-1000 ppm of In as a negative electrode active material for an alkaline storage battery, an amount of a gas generated and a rate of abnormal discharge generated in an intermittent discharge can be reduced in well balance and the provision of an alkaline battery of improved stability is possible.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a negative electrode active material used in an alkaline battery, and more particularly, to an alloy composition of zinc powder containing zinc as a main component, which contains less than 10 ppm of Al and 10 to 1%.
A negative electrode active material for an alkaline battery, which has less abnormal discharge during intermittent discharge and less gas generation, and an alkali using the same, by adjusting to a zinc alloy composition comprising 000 ppm Bi, 100 to 1000 ppm In, and other accompanying impurities. Battery.

[0002]

2. Description of the Related Art Zinc has been favorably used as a negative electrode active material for batteries because it has an appropriate potential when used as a negative electrode for batteries in an aqueous solution system and is inexpensive.
Since the corrosion potential of zinc is lower than the decomposition potential of water, hydrogen gas is generated when the zinc comes into contact with the electrolytic solution. That is,
In recent years, the development of zinc powder for batteries has focused on how to reduce the mercury-free zinc alloy and the resulting increase in gas generation due to environmental problems.

In order to solve this gas generation problem, various attempts have been made such as zinc alloy composition, zinc particle surface treatment, electrolytic solution composition, and addition of a corrosion inhibitor (inhibitor) to the electrolytic solution. In particular, Bi, In, Ga,
A zinc alloy containing several components of Sn, Pb, etc. and the composition ratio of these alloying elements are optimized with respect to the gas generation amount (JP-A-8-315816,
Japanese Patent Publication No. 7-54705, Japanese Patent Application Laid-Open No. 5-99082) has led to the launch of mercury-free alkaline batteries.

[0004]

However, at present, almost no improvement in battery characteristics such as a decrease in discharge capacity due to a discharge rate or a use condition viewed from a zinc negative electrode has been reported. Among these, regarding the short circuit due to zinc negative electrode deposits and the rapid decrease in discharge capacity during intermittent discharge repetition, it is believed that the essential cause is zinc powder, but generally satisfactory characteristics are not obtained. Hard to say. Accordingly, an object of the present invention is to provide a negative electrode active material for an alkaline battery and a battery using the same, in which the occurrence of abnormal discharge (short circuit, decrease in discharge capacity) during intermittent discharge is reduced while maintaining the gas generation amount at or below the current level. Is to provide.

[0005]

Means for Solving the Problems As a result of intensive studies for solving the above problems, it has been found that the negative electrode active material for an alkaline battery contains less than 10 ppm of Al, 10 to 1000 ppm of Bi, 100 to 1000 ppm of In, and other accompanying impurities. The present inventors have found that the use of zinc powder made of can significantly reduce abnormal discharge during intermittent discharge without increasing the amount of gas generation as compared with conventional products.

That is, the present invention firstly comprises zinc as a main component and less than 10 ppm of Al and 10 to 1000 ppm of B
a zinc alloy powder for an alkaline battery, comprising i, a zinc alloy powder containing 100 to 1000 ppm of In and other accompanying impurities; secondly, using the negative electrode active material according to the first aspect. An alkaline battery is provided.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The zinc powder of the present invention has an Al: 10p
pm, Bi: 10-1000 ppm, In: 100
It is produced by adding to molten zinc in the range of ~ 1000 ppm, alloying by stirring and mixing, and then atomizing with compressed air. The zinc powder thus produced can not only significantly reduce the generation of hydrogen gas, which is a characteristic conventionally required for mercury-free zinc powder for alkaline batteries, but also as a negative electrode active material for alkaline batteries. When used, the abnormal discharge occurrence rate at the time of intermittent discharge can be significantly reduced.

The mechanism of suppressing the generation of hydrogen gas and the suppression of abnormal discharge during intermittent discharge of the zinc powder composition are not clear at present, but are presumed as follows. Since zinc is a metal lower in potential than the decomposition potential of water, when it comes into contact with a strongly alkaline electrolyte, the following reaction occurs to generate hydrogen gas. ^{_{Zn + 2H 2 O + 2OH -}} = Zn (OH) 4 2- + H 2 ↑ ···

Although the reaction of this formula cannot be avoided in terms of equilibrium theory, the dissolution rate of zinc (= hydrogen gas generation) can be reduced to a level that can be practically used by corrosion treatment such as alloying and addition of an inhibitor. In the present invention, Bi and In having a high hydrogen overvoltage are used as alloying metals in amounts of 10 to 1000, respectively.
Gas generation is suppressed by adding 100 ppm to 100 ppm. If the content is less than 10 ppm and 100 ppm, respectively, no effect is exhibited. If the content exceeds 1000 ppm, not only the battery capacity is reduced but also the effect of increasing the addition amount is saturated. In addition, hydrogen overvoltage is low and seemingly unrelated 30p
This test confirmed that the addition of Al at pm or less has an effect of assisting the gas generation suppressing effect of the high hydrogen overvoltage metal, as shown in Examples described later.

[0010] intermittent discharge time of anomalies discharge discharge reaction _{^{Zn + 4OH - = Zn (OH}} ) 4 2- + 2e - ·· type discharge reaction generated by Zn ^{_(OH) 4 2-} ion with its concentration below formula Reaction proceeds, and Zn (O
H) ₄ ^2- → Zn (OH) ₂ → ZnO. Zn (OH) ₄ ^2- → Zn (OH) ₂ + 2OH ⁻ ·· Zn (OH) ₂ → ZnO + H ₂ O ...

At the time of discharge, the pH near zinc decreases according to the formula and the concentration of zinc ions increases, and the reaction proceeds to ZnO according to the formula. At the time of non-discharge, the diffusion of each ion proceeds into the electrolyte and the pH near zinc increases. Since the increase and the decrease of the zinc ion concentration occur, the dissolution of ZnO proceeds.

Namely, when subjected to intermittent discharge ^{_{Zn (OH) 4 2- = ZnO}} + H 2 O + 2OH - ··

[0013] Because of the equilibrium reaction of the above formula, the dissolution and precipitation of ZnO are repeated during discharge and during non-discharge, so that hollow needle-like crystals that grow in a specific orientation while repeating recrystallization of ZnO crystals are generated. The acicular ZnO grows in the direction of the positive electrode as the intermittent discharge cycle proceeds, and eventually penetrates through the separator to cause a short circuit with the positive electrode, resulting in abnormal discharge such as a sharp drop in voltage. In order to prevent abnormal discharge at the time of intermittent discharge, it is essential to suppress the growth of acicular ZnO. However, the present inventors have optimized acicular ZnO by optimizing the zinc alloy composition.
It has been found that it is possible to reduce the abnormal discharge at the time of intermittent discharge.

More specifically, as shown in Example 2 to be described later, the alloying ratio of Al is considered to have an effect of assisting the gas generation suppression effect of high hydrogen overvoltage metals Bi and In by the gas generation. It has been found that abnormal discharge at the time of intermittent discharge can be reduced by desirably setting it to less than 10 ppm.

[0015] If the composition is within the above range, a zinc powder having a gas generation amount that does not cause a practical problem can be obtained. That is, according to the zinc powder of the present invention, it is possible to reduce both the amount of hydrogen gas generated due to the zinc powder and the occurrence of abnormal discharge during intermittent discharge in a well-balanced manner. Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples. However, the composition of the alloyed zinc powder and the mixed metal powder used in the present invention are not limited to those used in the following examples.

[0016]

Example 1 As shown in the samples shown in Table 1, alloyed zinc composition Bi: 0 to 500 (ppm), Al: 0 to 30 (pp
m), In: 500 (ppm), particle size: 78 to 850
(Μm) of each sample No. Nos. 1-35 were produced by the atomizing method. This alloyed zinc powder was saturated with zinc oxide 4
A 0% -KOH electrolytic solution was added, the temperature was kept at 60 ° C., and the gas generation amount was calculated based on the gas generation amount on the third day (unit: μl).
/ G · day).

FIG. 1 shows the relationship between the amounts of alloyed Bi and Al and the amount of gas generated. It can be seen from FIG. 1 that the larger the amount of Bi added, the smaller the amount of gas generated regardless of the Al composition.
However, when the Al addition amount is 0 ppm, the Bi addition amount is 200 p.
If not more than pm, the gas generation amount is 20 μl / g · da
When the amount of Al added was 5 ppm and 30 ppm, the amount of gas generation was 2 at the amount of Bi added 80 ppm.
It is about 0 μl / g · day.

That is, a small amount of Al of 30 ppm or less
It was found that the addition was effective in suppressing gas generation, and that the addition of Al was effective even at about 5 ppm.

[0019]

Example 2 The same sample as in Example 1 was obtained by adding 40 wt% -K
After mixing with an OH electrolyte and a gelling agent, the LR6 type alkaline battery was charged to produce a sealed battery. The battery thus produced was discharged under the following discharge conditions (intermittent discharge), and the abnormal discharge occurrence rate was measured. (Discharge conditions) Resistance: 3.9Ω Discharge time: 5 minutes Discharge pause time: 11 hours and 55 minutes after discharge Discharge end voltage: 0.6 V

When the discharge voltage was lower than 0.9 V within 45 cycles of the above discharge cycle, abnormal discharge was determined. FIG. 2 shows a diagram of the amount of added Al and the occurrence rate of abnormal discharge. Above 30 ppm Al, the abnormal discharge occurrence rate was as high as 53%, whereas below 5 ppm Al, the abnormal discharge occurrence rate was remarkably improved to 3.1%.

[0021]

[Table 1]

[0022]

Comparative Example As is clear from the description of Example 1 and Example 2, in Table 1 showing the zinc powder composition, Al was 10%.
ppm, Bi is 10 to 1000 ppm, In is 10
All samples which do not correspond to the composition of 0 to 1000 ppm are understood as comparative samples.

[0023]

As described above, the negative electrode active material for an alkaline battery according to the present invention comprises zinc powder containing less than 10 ppm of Al and 10 to 10 ppm.
1000 ppm Bi and 100-1000 ppm In
Alkaline battery that can be reduced in both the amount of generated gas and the rate of abnormal discharge during intermittent discharge in a well-balanced manner, and has remarkably improved storage, safety and stability as a battery. Can be provided.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the amount of Bi and Al added to an alloyed zinc powder and the amount of generated gas in Examples of the present invention.

FIG. 2 is a graph showing the relationship between the amount of Al added to an alloyed zinc powder and the abnormal discharge occurrence rate in Examples of the present invention.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Yoshikazu Maeda 1-8-2 Marunouchi, Chiyoda-ku, Tokyo Dowa Mining Co., Ltd. (72) Inventor Masayoshi Matsumoto 1-8-2 Marunouchi, Chiyoda-ku, Tokyo Same as above F Mining in WA Mining Co., Ltd. (Reference) 5H003 AA03 AA10 BB02 BC01 BD04 5H015 AA02 DD01 EE05 HH01 5H024 AA14 FF38 HH01

Claims (2)

[Claims] 1. A composition containing zinc as a main component and less than 10 ppm of A
l and Bi of 10 to 1000 ppm and 100 to 1000 p
A negative electrode active material for an alkaline battery, comprising a zinc alloy powder containing pm of In and other accompanying impurities. 2. An alkaline battery using the negative electrode active material according to claim 1.