JPS5931834B2 - Hydrogen storage electrode - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is an improvement in an electrode having a hydrogen storage capacity, for example, an electrode used in a battery that generates electrical energy through an electrochemical reaction between the hydrogen stored in the electrode and oxygen. Regarding.

Conventionally, storage batteries such as lead-lead oxide and nickel-cadmium are known, but because these batteries contain active materials in the negative electrode, they have the disadvantage that their energy storage capacity per unit of weight or capacity is relatively low. Ta.

In order to improve this energy storage capacity, CaNi5, LaN, which absorbs hydrogen as a cathode that does not hold an active material,
Electrodes such as i, etc. have been proposed.

The CaNi5 alloy has a large initial discharge capacity but a relatively short cycle life, while the LaNi alloy has a relatively long cycle life but a small initial capacity. Conventionally, cathodes for storage batteries have been desired to have a large discharge capacity and a long cycle life. Therefore, the present invention focused on the long-life property of La atoms, A hydrogen storage electrode having a large initial discharge capacity and a long cycle life is provided by replacing a portion of the hydrogen atoms with La atoms, thereby eliminating the above-mentioned conventional drawbacks.

One embodiment will be described in detail below. Calcium (purity 99.5% or more) and lanthanum (purity 99% or more)
The atomic ratio of Ca:La is 1.0:ON0.8:0.
2, 0.6:0.4, 0.4:0.6, 0.2゛:0.
8. Weigh and mix each sample so that the ratio is 0:1.0, and then add nickel to this mixture so that the atomic ratio is 5 to 1. 10-
After vacuuming to 5To to remove oxygen gas adhering to the alloy, an arc is struck in an argon gas atmosphere (under reduced pressure) to heat and melt.

This operation is repeated several times to homogenize the sample. The obtained alloy was ground into a fine alloy powder in an Ar atmosphere, and the powder was sieved to a size of about 40 μm or less.

The alloy powder obtained in this way was filled into a leaded foam metal (a metal with open cell-like spaces and a porous body formed in a three-dimensional network shape), and
℃, l hour sintering to give Ca, -xLaxNi, (x=1~
0) system alloy sintered body was produced, and then this alloy sintered body was pressurized at about 200 kg/d to form a cathode.

The size of the cathode is 50 x 40n and the thickness is 1.5□, and the alloy powder as an active material is filled in about 59% per sheet, and the nickel powder as a conductive material is mixed before sintering. The aim was to improve electrode resistance.

The porous alloy obtained as described above was used as the cathode 1, a known nickel oxide was used as the anode 2, and the electrodes were immersed in an alkaline electrolyte 3 to construct the alkaline storage battery shown in FIG. In FIG. 1, 1 is a cathode, 2 is an anode, 3 is an electrolyte, 4 is a cathode lead plate, 5 is an anode lead plate, 6 is a separator, and 7 is a cathode.
is a battery container, and 8 is a liquid injection tap. The initial discharge capacity of this storage battery was measured using a 200 mA discharge current, and the results were as shown in FIG.

This result shows that as Ca atoms are replaced by La atoms, the initial discharge capacity decreases significantly, and the CaNi5 alloy (x
= 0)), the initial discharge capacity of the LaNi5 alloy (when x = 1.0) is 0.05 AFVf! When considering a practical alkaline storage battery that is very small (active material), it is necessary to have an initial discharge capacity of at least 0.25Ah/9.
In the substitution of La atom for a atom, the value of x is preferably 0.5 or less. On the other hand, the result of measuring the cycle life of this storage battery is the third
It was as shown in the figure. This result shows that the cycle life increases significantly as Ca atoms are replaced by La atoms, and while the cycle life of CaNi alloy (when x = 0) was about 65 cycles, the cycle life of LaNi5 alloy (x
= 1.0), the cycle life is greatly improved to approximately 300 cycles, and when considering a practical alkaline storage battery, the cycle life requires at least 150 cycles. Therefore, the substitution of La atoms for Ca atoms will increase the value of x. is preferably 0.05 or more.

From the above results, the optimal range that is practically preferable is Ca
The value of X in l-XLaXNi5 alloy is 0.05 to 0
．． It becomes 5.

When the value of x is 0.05 or less, the cycle life is too short, and when the value of x is 0.5 or more, the initial capacity is too small, and in either case, the battery cannot be used as a practical storage battery.

In addition, an excessive amount of La causes problems in terms of cost, so it is important to exhibit sufficient characteristics with as little La as possible. The following may be the reason why the cycle life is extended by replacing a portion of Ca atoms with La atoms. CaNl5 alloy exhibits high discharge capacity by absorbing a large amount of hydrogen at once from the beginning, but during repeated cycles, the crystallinity of the Cacu5 type structure partially collapses and reacts with KOH in the electrolyte, causing Ca (0H)2
The electrode itself expands due to hydrogen absorption, increasing internal resistance and shortening the cycle life. Now CaNi
When some of the Ca atoms in the 5 alloy are replaced by La atoms, C
aCu, the crystallinity of the type structure becomes less likely to collapse, and the expansion of the electrode itself is reduced. By replacing with 0, that is, La atoms, the electrode itself gradually becomes more difficult to absorb due to the effect of suppressing the absorption of a large amount of hydrogen at once in the initial stage. When activated, the initial capacity decreases a little, but it has the effect of extending the cycle life. This can be inferred from the fact that the LaNl5 alloy initially has a low hydrogen storage capacity and requires time for activation. As described above, the present invention improves both the initial discharge capacity and the cycle life of a hydrogen storage electrode by using a Cal-XLaXNi5 alloy in which some of the Ca atoms of the CaNi5 alloy consisting of calcium and nickel are replaced with La atoms. It is of great industrial value.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of an alkaline storage battery using a hydrogen storage electrode according to an embodiment of the present invention, FIG. 2 is an initial capacity characteristic diagram,
FIG. 3 is a cytal life characteristic diagram.

Claims (1)

[Scope of Claims] 1. A hydrogen storage electrode comprising a Ca_1_-_xLa_xNi_5 alloy in which some of the Ca atoms of the CaNi_5 alloy are replaced with La atoms. 2. The hydrogen storage electrode according to claim 1, wherein the value of 2x is in the range of 0.05 to 0.5.