JPH08102320A - Storage method for hydrogen storage alloy for alkaline storage battery - Google Patents

Abstract

PURPOSE: To prevent oxidation of a hydrogen storage alloy and drop in alloy activity by storing the hydrogen storage alloy with immersed in a surfactant- containing aqueous solution. CONSTITUTION: A mixture of a rare earth element, Ni, Co, Al, and Ma in a ratio of 1:3.4:0.8:0.2:0.6 is melted in a high frequency melting furnace kept in an inert gas atmosphere to manufacture a hydrogen storage alloy ingot. The alloy ingot is crushed in an inert gas atmosphere, and the alloy powder obtained is immersed in a surfactant-containing aqueous solution and stored at a specified temperature. Hydrophilic groups of the surfactant are oriented on the outside and adsorbed on the surface of the hydrogen storage alloy particle, and globular micelles using an alloy particle as a nucleus are formed and cover the alloy particle. Thereby, contact of the hydrogen storage alloy with oxygen or hydrogen ion existing in the aqueous solution is prevented.

Description

Detailed Description of the Invention

[0001]

The present invention relates to the reversible storage of hydrogen,
Regarding a method for storing a hydrogen storage alloy that can be released,
Specifically, it relates to a method of storing a hydrogen storage alloy for alkaline storage batteries in water.

[0002]

2. Description of the Related Art Generally, a process for producing a hydrogen storage alloy electrode comprises a step of finely pulverizing a hydrogen storage alloy ingot. However, in view of production efficiency, a certain amount of alloy ingot is produced in the pulverizing process. It is crushed at once. Therefore, it is necessary to store the finely pulverized hydrogen storage alloy powder at least until the next step is performed.

However, since the finely pulverized hydrogen-absorbing alloy powder has a remarkably high activity as compared with the alloy ingot, it reacts with oxygen and the like and is easily deteriorated under poor storage conditions. Further, if the oxidation reaction progresses at an accelerated rate, there is a risk of powdery particle explosion. For this reason, conventionally, the hydrogen storage alloy powder is stored by a method of dipping and storing in an organic solvent or a method of dipping and storing in water, and these methods can easily shield the alloy powder from the external environment. It is a simple and useful method. In particular, the method of dipping and storing in an organic solvent can effectively prevent oxidation if the organic solvent is properly selected. However, the number of organic solvents that do not adversely affect the hydrogen storage alloy and that can be easily removed after the end of storage is limited. Moreover,
The organic solvent generally has a risk of ignition and explosion, and also has a risk of deteriorating the health of workers, so that there is a problem in handleability and workability.

On the other hand, the method of immersion storage in water does not have the problems of organic solvents and is excellent in workability and safety. However, the water storage method has a problem that when the storage period is long, the alloy surface is gradually oxidized by dissolved oxygen and hydroxide ions, and the alloy activity is lowered.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and even when hydrogen-absorbing alloy powder is stored in water, oxidation of the alloy and deterioration of alloy activity are caused. It is intended to provide a storage method capable of preventing the above.

[0006]

In order to achieve the above object, the invention of claim 1 is a method for storing a hydrogen storage alloy for an alkaline storage battery, which stores the hydrogen storage alloy in water, wherein the storage method is a surfactant. It is characterized in that the hydrogen storage alloy is immersed and stored in an aqueous solution containing a surfactant added with.

According to a second aspect of the present invention, in the method for storing a hydrogen storage alloy for alkaline storage batteries according to the first aspect, the content of the surfactant in the aqueous solution containing the surfactant is 1 with respect to the weight of the hydrogen storage alloy to be dipped. It is characterized in that it is about 10 ⁴ ppm. The invention of claim 3 is the method for storing a hydrogen storage alloy for an alkaline storage battery according to claim 1 or 2, wherein the surfactant is an anionic surfactant.

[0008]

In the present invention having the above-mentioned structure, since the surfactant is added to the water in which the hydrogen storage alloy is dipped, the surfactant prevents the hydrogen storage alloy from being oxidized and prevents the alloy activation degree from being lowered. Act on. The reason why the surfactant exerts such an action effect is considered to be as follows. That is, when the hydrogen-absorbing alloy powder is immersed in a surfactant-containing aqueous solution, the surfactant is adsorbed on the surface of the hydrogen-absorbing alloy particles by orienting the hydrophilic groups to the outside, and the spherical micelle-like particles having the alloy particles as cores are formed. To form one. Since this covers the periphery of the alloy particles, contact between the hydrogen storage alloy and oxygen or hydroxide ions dissolved in water is hindered. In other words, the micelle-like thing,
It serves as a barrier for the alloy surface and prevents oxidation of the alloy surface due to dissolved oxygen and the like. Note that the present inventors have confirmed that when the hydrogen storage alloy is stored for a long period of time in water containing no surfactant, acicular hydroxide on the alloy surface is produced.

In the above, the amount of the surfactant added to the alloy preservation aqueous solution is preferably 1 to 10 ⁴ ppm with respect to the total weight of the hydrogen storage alloy to be immersed. This is because in this addition range, the antioxidant effect on the hydrogen storage alloy is efficiently exhibited in relation to the addition amount, and the adverse effect on the electrode reaction due to the addition of the surfactant can be avoided. The surfactant used may be any of anionic, cationic, nonionic and amphoteric types, and the type thereof is not particularly limited.
However, the anionic surfactant is excellent in the surfactant effect,
It is also preferable because it is considered to form a barrier suitably. The reason why good results are obtained when the amount of the surfactant added is within the above range is considered to be as follows. That is, when the amount of the surfactant added is less than 1 ppm, the amount of the surfactant is insufficient with respect to the total specific surface area of the hydrogen storage alloy particles, and thus a sufficient barrier cannot be formed on the surface of the alloy particles. On the other hand, the amount of surfactant added is 10 ⁴ pp
When m is exceeded, a barrier is formed, but the amount of the surfactant remaining in the alloy increases, and it is considered that this residual surfactant hinders the electrode reaction. However, even if the addition amount of the surfactant is out of the above range, it is needless to say that the oxidation of the hydrogen storage alloy is suppressed as compared with the case where the surfactant is not added.

[0010]

【Example】

[Example] Mm (mixture of rare earth elements): Ni: Co:
The respective metal elements of Al: Mn are 1: 3.4: 0.8: 0.
2: 0.6 ratio by taking into high-frequency melting furnace with an inert gas atmosphere, melted and the composition formula MmNi _3.4 Co _0.8 Al
A hydrogen storage alloy ingot represented by _0.2 Mn _0.6 was produced, and the alloy ingot was made to have an average particle size of 150 μm in an inert gas atmosphere.
The powder was pulverized to give a hydrogen storage alloy powder for alkaline storage batteries.

1000 g of this hydrogen storage alloy powder was added to water 2
Each of them was immersed in 10 kinds of aqueous solutions containing a surfactant (1000 ppm with respect to the alloy) in which 1 g of the surfactant shown in Table 1 was added to 00 g and stored at a liquid temperature of about 25 ° C. for 30 days. [Comparative Example] The hydrogen-absorbing alloy powder produced in the example was immersed and stored in water containing no surfactant under the same conditions as above for 30 days.

[Experiment 1] The oxygen concentration and the degree of activation of the alloys of the example alloy powder (stored in a surfactant-containing aqueous solution for 30 days) and the comparative alloy powder (stored in pure water for 30 days) were measured by the following method. The measurement was performed. The oxygen concentration and the degree of activation of the hydrogen storage alloy powder before the start of storage in water were also measured in advance by the same method.

Method for Measuring Oxygen Concentration and Degree of Alloy Activation The alloy oxygen concentration is measured by an oxygen analyzer (TC-4 manufactured by LECO).
36). In addition, the measurement of the alloy activation degree,
An electrode was formed by using the alloy powder before immersion storage, the example alloy powder, and the comparative example alloy powder, and a test cell was formed by the electrode, and the test was performed using this cell. The details are as follows.

First, 1.2 g of carbonyl nickel as a conductive agent and 0.2 g of polytetrafluoroethylene powder as a binder were added to 1 g of hydrogen-absorbing alloy powder and kneaded to prepare an alloy paste. It was wrapped with a nickel mesh and pressed to produce a hydrogen storage alloy electrode. Further, using this electrode, a test cell shown in FIG. 2 was prepared with a nickel electrode having a discharge capacity sufficiently larger than that of the electrode and a 30 wt% KOH aqueous solution.

Using the above test cell, the battery was charged with 50 mA / g-alloy for 8 hours and then discharged with 200 mA / g-alloy until the cell voltage reached 1.0 V. At this time, the discharge capacity C
1 was measured. On the other hand, for the same cell, 50 mA / g-
After being charged with the alloy for 8 hours, it was discharged with 50 mA / g-alloy until the cell voltage reached 1.0 V, and the discharge capacity C at this time
2 was measured. The activation degree was calculated from the C1 and C2 by the following formula. Degree of activation (%) = C1 / (C1 + C2) × 100 The structure of the test cell will be described below with reference to FIG. In FIG. 2, reference numeral 1 is a negative electrode, and the hydrogen storage alloy electrode formed in a cylindrical shape is installed on the negative electrode 1. 2 is a known sintered nickel electrode (positive electrode) manufactured by a known method, and this sintered nickel electrode 2 is held by a positive electrode lead 4 connected to an upper surface 5 of a closed container 3, The electrode 1 is held by a negative electrode lead 6 connected to the upper surface 5 of the hermetically sealed container 3 so as to be vertically positioned substantially in the center of the cylinder of the sintered nickel electrode 2. Further, the respective ends of the positive electrode lead 4 and the negative electrode lead 6 are connected to the upper surface 5 of the closed container 3.
Exposed to the outside and connected to the positive electrode terminal 4a and the negative electrode terminal 6a, respectively. A 30 wt% potassium hydroxide aqueous solution is put in the closed container 3 as an alkaline electrolyte, and the hydrogen storage alloy electrode 1 and the sintered nickel electrode 2 are immersed in this solution. 7 is a pressure gauge, 8 is a relief pipe, and 9 is a gas relief valve.

(Result of Experiment 1) Table 1 shows a list of measurement results of various alloy powders before starting storage in water in Examples and Comparative Examples.

[0017]

[Table 1] No. 1 to 10; Inventive example, No. 11; Comparative example As is clear from Table 1, the oxygen concentration of the hydrogen storage alloy powder of the comparative example was 0.10 Wt% before the start of immersion storage, but it was immersed in water for 30 days. It increased to 0.50 Wt% after storage. On the other hand, in the examples which were immersed and stored in a 1000 ppm (concentration based on alloy weight) aqueous solution containing a surfactant, the alloy oxygen concentration after storage for 30 days was 0.11 for each.
It remained within the range of 0.15 Wt%, and the increase in oxygen concentration was significantly suppressed.

On the other hand, regarding the activation degree of the alloy, in the comparative example, the activation degree of 80% before the start of immersion storage was 80%, but it was 35% after storage in water for 30 days (reduction rate 56.3).
%). On the other hand, in each of the examples, 7
It was 9% to 76% (reduction rate 1.3 to 5.0%), which was an extremely small reduction. From these results, it is possible to effectively prevent the oxidation of the hydrogen storage alloy by the method of dipping and storing the hydrogen storage alloy using the surfactant-containing aqueous solution, and therefore, the activation degree of the hydrogen storage alloy is significantly reduced. It turns out that it is suppressed. It is considered that the reason why such an effect is obtained by adding a surfactant is that a spherical micelle-like barrier is formed by the surfactant on the surface of the hydrogen storage alloy particles, and this barrier blocks oxygen. .

[Experiment 2] Next, in order to investigate the relationship between the surfactant concentration, the oxygen concentration (oxidation degree) of the alloy, and the alloy activation degree, sodium oleate was used as the surfactant and the concentration was adjusted to 0 Seven kinds of sodium oleate aqueous solutions were prepared by changing the concentration to 10 ⁵ ppm (concentration with respect to the immersion alloy amount), the hydrogen storage alloy powder was immersed and stored in these aqueous solutions under the same conditions as described above, and the same method as above. The oxidation concentration and activation degree of the alloy were measured by.

The results are shown in FIG. ●-● in Fig. 1
Indicates the relationship between the surfactant concentration and the oxygen concentration of the hydrogen storage alloy, and X ... X indicates the relationship between the surfactant concentration and the alloy activation degree. The surfactant concentration (horizontal axis) is on a logarithmic scale. From FIG. 1, it can be seen that even if the surfactant concentration is 1 ppm, the oxidation of the alloy can be suppressed, and as the surfactant concentration increases from 1 ppm to 10 ² ppm, the oxidation suppressing effect increases. However, if the surfactant concentration is 10 ²
When the concentration exceeded ppm, no further oxidation inhibitory effect was observed.

On the other hand, the effect of preventing the decrease in the degree of activation of the alloy is almost in line with the case of the effect of suppressing the oxidation up to 10 ² ppm, and the effect of preventing the decrease in the degree of activation increases as the concentration of the surfactant increases. It was However, when it exceeds 10 ³ ppm, unlike the case of the antioxidant effect, the activation degree tends to be sharply reduced, and when 10 ⁵ ppm is added, it is reduced to the same level as when it is not added.

From these results, the surfactant concentration was 1 pp.
m is preferably 10 to ⁴ ppm, more preferably 1 to 10 ³
It turns out to be ppm. The surfactant concentration is 10 ³
The alloy activation rate decreased sharply when the concentration exceeded ppm.
It can be considered as follows. That is, a surfactant barrier having a sufficient thickness (or density) capable of blocking the contact between the alloy and dissolved oxygen is completed at about 10 ² ppm, and beyond that, the effect is no longer enhanced. On the other hand, it is considered that the amount of the surfactant remaining on the alloy surface increases, and this residual surfactant inhibits the electrode reaction of the hydrogen storage alloy, so that the alloy activation degree is rather decreased.

[0023]

As described above, according to the method for storing a hydrogen storage alloy of the present invention, the surfactant present in the aqueous solution effectively prevents the hydrogen storage alloy from being oxidized. However, the reduction of the alloy activation degree can be suppressed. Therefore, according to the present invention, it is possible to provide a remarkable effect that it is possible to provide a method for storing a hydrogen storage alloy that is excellent in storability, workability, and safety.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the surfactant concentration of a stored aqueous solution, and the alloy oxygen concentration and the degree of alloy activation after storage for 30 days.

FIG. 2 is a diagram showing an outline of a test cell used for measuring the activation degree of a hydrogen storage alloy.

Claims (3)

[Claims] 1. A method of storing a hydrogen storage alloy for an alkaline storage battery, which comprises immersing and storing the hydrogen storage alloy in a surfactant-containing aqueous solution containing a surfactant. 2. The surfactant content of the surfactant-containing aqueous solution is 1 to 10 with respect to the weight of the hydrogen storage alloy to be immersed.
^The method for storing a hydrogen storage alloy for alkaline storage batteries according to claim 1, wherein the storage capacity is ⁴ ppm. 3. The method for storing a hydrogen storage alloy for alkaline storage batteries according to claim 1, wherein the surfactant is an anionic surfactant.