JPH05190173A - Hydrogen storage electrode - Google Patents

Abstract

PURPOSE:To provide a hydrogen storage electrode for forming a sealed battery which has the drastically less cell internal pressure generated in electric charge and can be manufactured relatively at low cost. CONSTITUTION:An electrode is made of the hydrogen storage alloy which is represented by a general formula MmNiaCobAlc (3.0<=a<=3.5, 0.7<=b<=1.3, 0.3<=c<=0.6, 4.0<=a+b+c<=5.2), and an La content in Mm of 80wt.% or more.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a hydrogen storage electrode used as a negative electrode of a sealed alkaline storage battery or the like.

[0002]

2. Description of the Related Art Conventionally, nickel-cadmium storage batteries have been most widely used as power sources for various electric and electronic devices. Although this battery is excellent in performance, the development of a new alkaline storage battery has been studied from the viewpoint of high energy density and pollution-free, and recently, a hydrogen storage alloy that reversibly stores and releases hydrogen is used as a negative electrode. Attention is paid to alkaline storage batteries. This battery is promising as a non-polluting alkaline storage battery with a high energy density, since a battery can be constructed in the same manner as a cadmium electrode and the actual dischargeable capacity density can be made larger than that of a cadmium electrode. The hydrogen storage alloy used as the negative electrode is LaNi ₅ , La.
La alloy-based materials such as Ni _4.5 Al _0.5 are known.

[0003]

However, when the above hydrogen storage alloy is used as the negative electrode of a sealed alkaline storage battery, there is an advantage that a high capacity can be obtained, but the internal pressure of the battery becomes extremely high during charging. However, there is a large tendency to shorten the battery life due to leakage of the electrolytic solution through the safety valve.

[0004]

The present invention solves the above-mentioned conventional problems and provides a hydrogen storage electrode for a sealed alkaline storage battery which can be manufactured at a relatively low cost and which can significantly reduce the internal pressure of the battery. Then, the solution is the general formula MmN
i _a Co _b Al _c , provided that 3.0 ≦ a <3.
5, 0.7 ≦ b ≦ 1.3, 0.3 ≦ c ≦ 0.6, 4.0
The hydrogen storage alloy is ≦ a + b + c ≦ 5.2, and the lanthanum content in Mm is 80% by weight or more.

[0005]

[Function] A sealed alkaline storage battery using a hydrogen storage alloy having the above-mentioned structure and a hydrogen storage electrode prepared by a conventional method and using this as a negative electrode is not clear for the reason, but the internal pressure of gas generated during charging rises. Can be kept small.

[0006]

EXAMPLES In order to clarify the features of the present invention, the examples will be described in detail together with comparative examples and conventional examples. Commercially available M
m (La: 87 wt.%, Ce: 2 wt.%, Nd: 9
wt. %, Other rare earth metals: 2 wt. %), Ni,
Co and Al were weighed and blended in the composition ratios shown in Table 1 below, and then each was heated and melted in an argon arc melting furnace to prepare alloys having the respective composition ratios. Next, each of these alloys was mechanically pulverized to 100 μm or less to produce a hydrogen storage alloy powder having various compositions. To each of the hydrogen storage alloy powders, 10% by weight of Ni powder as a conductive agent and 2% by weight of fluororesin powder as a binder were added and mixed to form a fluorine resin fiber, which was then crushed to obtain a mixture. Was pressure-molded on a nickel wire mesh at 1 t / cm ² to prepare various hydrogen storage alloy electrodes. Each of these various hydrogen storage alloy electrodes was used as a negative electrode, a known paste type nickel electrode was combined as a positive electrode, and a 30% potassium hydroxide solution was used as an alkaline electrolyte to prepare a cylindrical closed cell of AA size 1000 mAh. These cells are designated as cell No. 1 in Table 1. 3 to 16 are shown. A pressure sensor was attached to each cell for the purpose of measuring the cell internal pressure during charging.

For comparison, a cell using a conventional hydrogen storage electrode was manufactured as follows. That is, pure La, Ni, and Al were used as raw materials, and these were weighed and blended at the composition ratios shown in Table 1, and two kinds of conventional hydrogen storage alloy powders were produced in the same manner as described above. Using each of the hydrogen storage alloy powders, each hydrogen storage alloy electrode was produced in the same manner as described above. Using these conventional electrodes as negative electrodes, an AA size 1000 mAh cylindrical closed cell was prepared in the same manner as described above. These cells are designated as cell No. 1 in Table 1. 1 and No. 1 2 shows. A pressure sensor was attached to each cell for the purpose of measuring the cell internal pressure during charging.

These cell Nos. For 1 to 16,
450% (4.5%) of the rated capacity at 1C (1A) current, respectively.
Time) The cell internal pressure when charged was measured. The measurement results were as shown in Table 1.

[0009]

[Table 1]

From the practical point of view, the cell internal pressure is 20 at maximum.
It is desirable to be able to suppress it to Kgf / cm ² . From this point, these cell Nos. 1-No. When the cell internal pressures of the respective 16 cells are compared and examined, as is clear from Table 1, the conventional cell number. 1 and No. 1 No. 2, the cell internal pressure was extremely high, exceeding ²⁰ Kgf / cm ² , and
It is very problematic in practical use. In addition, the cell No. 11-N
o. In No. 16, the internal pressure is lower than that of the conventional cell, but it is 21 Kgf / cm ² or more, which is still insufficient in practical use. On the other hand, cell No. 3 to No. No. 10 has an internal pressure of 20 Kgf / cm ² or less, and there is no practical problem. These cell No. 3 to No. The hydrogen storage alloy used as the hydrogen storage electrode used in No. 10 is the cell N
o. 11-No. As is clear from comparison with No. 16, the following alloy composition conditions are entered. That is, MmNi _a Co _b Al
_In the general formula of _c , 3.0 ≦ a <3.5, 0.7 ≦ b
≦ 1.3, 0.3 ≦ c ≦ 0.6, respectively,
Also, it corresponds to _X of ABX, that is, the condition of 4.0 ≦ a + b + c ≦ 5.2, and the cell internal pressure is 20 Kg due to such alloy composition
It was confirmed that it was suppressed to f / cm ² or less.

Next, in the above alloy composition, the following comparative test was conducted in order to examine the influence on the cell internal pressure when the content ratio of La is changed among various rare earth metals constituting the misch metal. went.

Next, in order to examine the change in the content of lanthanum (La) in the misch metal Mm forming the hydrogen storage alloy forming the hydrogen storage electrode of the above-mentioned embodiment and the influence thereof on the internal pressure of the cell, first, MmNi _3.49 Co _1.00 Al _0.50 having different La contents as follows.
A hydrogen storage alloy having a composition of was prepared.

That is, the above cell No. Hydrogen storage alloy MmNi _3.49 Co _1.00 Al _0.50 (M
La content in m of 87 wt. %), Commercially available La:
45 wt. %, Ce: 4 wt. %, Nd: 36 wt.
%, Pr: 12 wt. %, Other rare earth metals: 3w
t. % Of Mm, La: 25 wt. %, Ce: 49
wt. %, Nd: 17 wt. %, Pr: 6 wt. %, Other rare earth metals: 3 wt. % Consisting of Mm and other M
Various commercially available Mm whose content in m is different from the above, and also
A proper amount of pure La is mixed with Mm to make La in Mm 5
0 wt. %, 55 wt. %, 60 wt. %, 65 wt.
%, 70 wt. %, 75 wt. %, 80 wt. %, 85
wt. %, 90 wt. %, 95 wt. %, Prepared various Mm and prepared Ni, Co, Al for each Mm.
Weighed and blended with a constant composition ratio, heated and melted in a melting furnace,
MmNi _3.49 Co _1.00 Al with different La contents
Various alloys consisting of _0.50 were made, and each alloy was
Each hydrogen storage alloy powder was manufactured by pulverizing to a particle size of less than 00 μm.

Using these alloy powders, hydrogen storage electrodes were prepared in the same manner as described above, closed cells were prepared in the same manner as described above using the respective electrodes as negative electrodes, and charged in the same manner as described above. The internal pressure of each cell was measured. The result was as shown in FIG.

As is apparent from FIG. 1, the cell internal pressure is set to 20
In order to suppress it to Kgf / cm 2 or less, the content ratio of La in Mm is 80 wt. It was found to be over%. As can be seen from FIG. 1, as the La content in Mm approaches 100%, the decrease in cell internal pressure was observed. Therefore, in place of Mm, pure La corresponding to La content of 100% is used as a raw material, and Ni, Co, and Al are weighed and mixed in the above composition ratio, and LaNi _3.49 Co _1.00 Al _0.50 alloy A cell having the above-mentioned electrode as a negative electrode has the greatest effect in reducing the internal pressure of the cell, but since the La is expensive, the manufacturing cost of the alloy increases, which is disadvantageous. On the other hand, Mm
Has a La content of about 80 wt% to 90 wt. % Hydrogen peroxide is commercially available and can be obtained at low cost, which is advantageous because the hydrogen storage electrode can be manufactured at low cost.

[0013]

As described above, according to the present invention, it is represented by the general formula MmNi _a Co _b Al _c , where 3.0 ≦ a <
3.5, 0.7 ≦ b ≦ 1.3, 0.3 ≦ c ≦ 0.6,
4.0 ≦ a + b + c ≦ 5.2 and La in Mm
The content is 80 wt. When a hydrogen storage alloy having a hydrogen storage alloy content of not less than 10% is used as the hydrogen storage electrode, it has an effect of obtaining an inexpensive sealed battery having a small cell internal pressure.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the La content in the composition element Mm of the hydrogen storage alloy used as the negative electrode of a sealed battery and the cell internal pressure.

Claims (1)

[Claims] 1. A compound represented by the general formula MmNi _a Co _b Al _c , provided that 3.0 ≦ a <3.5, 0.7 ≦ b ≦ 1.3,
A hydrogen storage electrode made of a hydrogen storage alloy having 0.3 ≦ c ≦ 0.6, 4.0 ≦ a + b + c ≦ 5.2, and a lanthanum content in Mm of 80% by weight or more.