JPS61203561A - Battery electrode - Google Patents

Abstract

PURPOSE:To improve the flatness of the discharge curve of the negative electrode of an alkaline storage battery or a similar battery and to increase its cycle life by forming the negative electrode from an alloy represented by general formula LnNialphaMnbeta which is thermally treated at a temperature below the melting point of the alloy. CONSTITUTION:A hydrogen occlusion alloy which can electrochemically occlude or release hydrogen is used as the negative electrode for an alkaline storage battery or a similar battery. The negative electrode is made by heating an alloy represented by general formula LnNialphaMnbeta (Ln is lanthanum or a Misch metal containing lanthanum.; 4<alpha+beta<5.5; 0<beta) either in a vacuum or in an atmosphere of an inactive gas or hydrogen gas at a temperature of at least 900 deg.C for at least 1hr. As a result, the homogeneity of the alloy is improved and hydrogen occluded into the alloy remains in a constant energy state. Therefore, it is possible to improve the flatness of the discharge curve and to increase the cycle life of the electrode.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a battery electrode using a hydrogen storage alloy capable of electrochemically absorbing and desorbing hydrogen as a negative electrode.

Lead-acid batteries and nickel-cadmium batteries have been well known in the past, but these batteries have the disadvantage of having a relatively low energy density per unit of weight or volume. Therefore, a nickel-hydrogen storage battery with high energy density has been proposed, which uses an alloy that can electrochemically absorb and release large amounts of hydrogen as the negative electrode and nickel oxide as the positive electrode.

For the negative electrode, L al'J is, LaNi4Cu,
LaNi4Co.

Hydrogen storage alloys such as L aN i4.7AR0,3 were used (for example, Japanese Patent Publication No. 59-49671)
. However, these alloys have the disadvantage of a small discharge capacity (50 mAh/r to 200 mAh/?) at high temperatures (46° C.). Therefore, in order to improve the characteristics especially at high temperatures, LaNi4.26Mn0.76 (Int, Sym
p, Hydro Energy Storage
P, 486 (197B)) was used.

Problems to be solved by the invention However, in this case, L aN i4.2sMno,
7s has a problem in that the flatness of the discharge curve is poor and the discharge capacity decreases after several tens of charging and discharging cycles.

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention provides a negative electrode of a battery using a heat-treated β alloy of the general formula L nN i-
This provides a battery with good discharge curve flatness and excellent cycle life.

Effect LnNiaMu β(4(α+β(5,6,0(β,
Mitsushmetal containing La alone or La f) heat treatment'f, 7Il! The uniformity of the alloy is improved by increasing the temperature. Therefore, no heat treatment is performed.

Compared to alloys, occluded hydrogen exists in alloys in a more constant energy state.

As a result, the flatness of the discharge electrode curve, which means the total release of hydrogen in the alloy, becomes good. Furthermore, since a very uniform alloy is formed by heat treatment, it is stable even in an alkaline electrolyte, and the discharge capacity does not decrease with repeated charge/discharge cycles, resulting in an electrode with excellent cycle life.

EXAMPLES The present invention will be explained below with reference to Examples. Mitsushmetal (a mixture of rare earth elements, e.g. Ce 45 wt%, La 30 wt%, Nd
5wt%, etc.) Nickel and manganese K were mixed at a certain composition ratio, placed in an arc melting furnace, and 10. ""~1O-5
After creating a vacuum state until the temperature reached 1, arc discharge was performed in an argon gas atmosphere (reduced pressure state) to heat and melt. This operation was repeated four times to prepare an alloy (untreated). Heat treatment is
The alloy obtained by arc melting was placed in a vacuum heat treatment furnace (1o-' to 1
The test was carried out at 1060° C. for 6 hours at 0-5 Torr. Third
As shown in the figure, the plateau pressure of the heat-treated alloy is very good, and it can be seen that the heat treatment has resulted in a very uniform alloy.

Next, after coarsely pulverizing these alloys, they were milled to 38 μm using a ball mill.
The following fine powder was made into a paste with a 5 wt % aqueous solution of polyvinyl alcohol, filled into a foamed metal, dried and pressurized (2 toh/m), and then the entire lead was attached as an electrode. The electrodes used in the experiment are shown in the table.

These electrodes were used as negative electrodes (alloy 32), and a mercury oxide electrode (Ht/Hf0) was used as a reference electrode. An example of the results of examining the flatness of the monopolar discharge curve is shown in FIG.

The charging and discharging conditions are charging 0.3A x 4hr and discharging 0.2A. As is clear from Figure 1, electrode (1) using a heat-treated alloy has a better flatness of the discharge curve than electrode (2) using an untreated alloy. . Although FIG. 1 only shows one example of the results, the electrodes shown in the table showed similar results.

Next, the results of examining the cycle life are shown in Figure 2 and the table. As is clear from FIG. 2 and the table, the cycle life characteristics are better when heat-treated alloys are used. When using an alloy (4) that has not been heat-treated, manganese is released due to repeated charging and discharging.
of discharge capacity dissolved in the liquid.

Deterioration occurs. The heat treatment temperature is 900 to 1200°C.
It is effective in a temperature range of 900C or lower, and the flatness of the discharge curve and the cycle life characteristics are not improved. Also,
At high temperatures of 1200C or higher, the alloy composition ratio changes due to heat treatment, resulting in an alloy with a small discharge capacity.

In the above embodiment, an alkaline storage battery was described, but it can also be used as a hydrogen storage electrode such as a negative electrode of a fuel cell.

Effects of the invention As described above, heat-treated tm LaN1 aan β (4〈
A negative electrode using an alloy represented by α+β<S, S, O<β) has a good discharge curve flatness and excellent cycle life characteristics. Therefore, an alkaline storage battery using the heat-treated alloy negative electrode has a flat discharge curve, an excellent cycle life, and is extremely useful in practice.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the discharge curve of an alkaline storage battery using an electrode sound according to an embodiment of the present invention, Fig. 2 is a diagram showing the cycle life of the same battery, and Fig. 3 is a diagram showing the P-C-T curve of the alloy. FIG. 3...Heat treatment, 4...No treatment. Name of agent: Patent attorney Toshio Nakao and 1 other person
1 Figure/-11 processing? ----Processing force (Electronic time CAK) Fig. 2 3--- Heat treatment - (Ltddi4sMha, 5) 4---
-2. processingflL(LttNi4..5Mrn05)o
5θ
lOθ charging/discharging cycle ridge (pheasant Fig. 3-5--Imtinct processing.

Claims (3)

[Claims] (1) General formula L heat treated at a temperature below the melting point of the alloy
nNi_αMn_β (Ln is lanthanum alone or misch metal containing lanthanum, 4<α+β<5.5,
A battery electrode characterized in that the negative electrode is equipped with an alloy represented by O<β). (2) The battery electrode according to claim 1, wherein the heat treatment is heating at a temperature of 900° C. or higher for 1 hour or longer. (3) The battery electrode according to claim 1, wherein the heat treatment is performed in vacuum, inert gas, or hydrogen gas.