JPH03295165A - Manufacture of hydrogen storage alloy electrode for alkaline storage battery - Google Patents

Abstract

PURPOSE:To prevent the reduction of the battery capacity and the reduction of the discharge voltage caused by the formation of an oxidized film on the surface of a hydrogen storage alloy by performing the crushing process of hydrogen storage alloy lumps and the kneading process of hydrogen storage alloy powder and a binder in an aqueous solution restricted with melted oxygen. CONSTITUTION:When hydrogen storage alloy lumps are crushed in an aqueous solution restricted with dissolved oxygen, oxidation is suppressed even on the very active alloy surface exposed by crushing. When hydrogen alloy powder and a binder are kneaded in the aqueous solution restricted with melted oxygen, the oxidation on the alloy surface during the kneading process can be suppressed. The dissolution of the oxidized film and alloy generated on the active alloy surface into the aqueous solution can be suppressed, and a hydrogen storage alloy electrode with an excellent characteristic is obtained. The aqueous solution has very excellent safety as compared with an inflammable solution such as an organic solvent.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a method for manufacturing a hydrogen storage alloy electrode for an alkaline storage battery that can reversibly store and release hydrogen.

(B) Conventional technology Storage batteries that have been commonly used in the past include alkaline storage batteries such as nickel-cadmium storage batteries, and lead storage batteries, but in recent years, batteries that are lighter, higher in capacity, and have higher energy density than these T batteries have been developed. Metal-hydrogen alkaline storage batteries, which have a negative electrode equipped with a hydrogen-absorbing alloy electrode made of a hydrogen-absorbing alloy, are attracting attention.

Hydrogen storage alloys used in the negative electrode of second type batteries include:
For example, as disclosed in Japanese Patent Publication No. 59-49671, LaNi and its improved three-element LaN
i4Cu, LaNi4Cu and L aN +4. aFe
Alloys such as a and t are known. A porous body obtained by sintering these alloy powders together with conductive material powder is used as a hydrogen storage alloy electrode (Japanese Patent Publication No. 1983-49669), or a mixture of these hydrogen storage alloy powders and conductive material powder is used as an electrolyte-resistant solution. A method of making a hydrogen-absorbing alloy electrode by fixing it to a conductive core using a particulate binder (Japanese Patent Publication No. 57-3027
Publication No. 3) etc. have been adopted.

Furthermore, as the positive electrode, a sintered nickel electrode used in nickel-cadmium storage batteries and the like is used.

In particular, a method of melting and pulverizing a hydrogen storage alloy to form a hydrogen storage alloy electrode is detailed in JP-A-60-250558. This is a hydrogen storage alloy obtained by weighing and mixing the metals used as raw materials for hydrogen storage alloys to a certain composition ratio, placing them in an arc melting furnace, subjecting them to arc discharge under a reduced pressure argon atmosphere, and heating and melting them. After coarsely grinding the ingot, it is made into fine powder using a ball mill. It is known that a conductive core is coated and filled with the hydrogen storage alloy fine powder obtained in this manner and a binder.

The second type, the hydrogen storage alloy electrode, reaches the end of its cycle life due to the hydrogen storage alloy being pulverized by repeated charging and discharging cycles, the electrode being deformed, and the hydrogen storage alloy falling off from the electrode.

Therefore, when using a hydrogen storage alloy for the negative electrode, the alloy should be pulverized before filling it into the conductive core to prevent further pulverization even as the battery charge/discharge cycle progresses. A method to do so is being considered.

There are two methods for pulverizing, or pulverizing, this hydrogen-absorbing alloy: a hydrogen pulverization method in which hydrogen is forcibly absorbed and released into the alloy and the alloy is pulverized, and a mechanical pulverization method in which the alloy is mechanically pulverized using a ball mill or the like. . The above-mentioned cell hydrogenation pulverization method cannot be said to be preferable in terms of mass production because it is not possible to pulverize a large amount of alloy at one time. On the other hand, in the mechanical pulverization method, the pulverized hydrogen storage alloy is active and therefore easily reacts with oxygen. Therefore, it has been proposed that pulverization be carried out in an inert atmosphere, in an organic solvent, or in an aqueous solution to suppress oxidation of the alloy surface (see, for example, Japanese Patent Application Laid-Open No. 141258/1983). Since pulverization requires a larger apparatus and is subject to various restrictions, it cannot be said to be preferable in terms of the electrode manufacturing process.

Furthermore, since pulverization in an organic solvent is difficult and dangerous in handling the organic solvent, it is preferable to use an aqueous solution.

However, when a hydrogen storage alloy is crushed in an aqueous solution, the surface of the alloy exposed by the crushing is oxidized by dissolved oxygen in the aqueous solution. Along with this, the aqueous solution becomes alkaline, and a new problem has arisen in that the alloy is eluted into the aqueous solution and the properties of the alloy are deteriorated.

(c) Problems to be Solved by the Invention The present invention has been made in view of the above-mentioned problems, and is intended to suppress oxidation of the alloy surface during crushing and kneading of hydrogen-absorbing alloy lumps.

The present invention is intended to solve the problem of a decrease in battery capacity and a decrease in discharge voltage caused by the formation of an oxide film on the surface of a water-X storage alloy.

(d) Means for Solving the Problems The method for producing a hydrogen storage alloy electrode for an alkaline storage battery of the present invention involves pulverizing a hydrogen storage alloy lump in an aqueous solution with regulated dissolved oxygen to produce hydrogen storage alloy powder f11. a crushing process;
(a) a kneading step for obtaining a kneaded product by kneading the hydrogen storage alloy powder and a binder in an aqueous solution with controlled oxygen content; and a filling step for filling the conductive core with the kneaded material. That is.

Further, in the pulverizing step and the kneading step, the amount of dissolved oxygen in the aqueous solution is desirably 19 mg71 or less.

Furthermore, the particle size of the hydrogen storage alloy powder in the pulverization step is preferably 150 mm or less.

Furthermore, it is preferable that the aqueous solution in which dissolved oxygen is regulated in the pulverizing step and the kneading step is 10% by weight to 100% by weight based on the weight of the hydrogen storage alloy.

As the binder, polyethylene oxide, hydroxypropyl cellulose, -borivinyl alcohol, carboxymethyl cellulose, methyl cellulose, Bottetrafluoroethylene which is a fluororesin powder, etc. can be used.

(e) Action When a hydrogen storage alloy block is crushed in an aqueous solution containing a large amount of dissolved oxygen, the alloy surface newly exposed by the crushing is extremely active and is therefore oxidized by the dissolved oxygen in the aqueous solution. As a result, the aqueous solution becomes alkaline, and the hydrogen storage alloy easily dissolves into the aqueous solution, degrading the hydrogen II & storage alloy performance in the electrode.

However, as in the present invention, by grinding in an aqueous solution with regulated dissolved oxygen, oxidation is suppressed even on the extremely active alloy surface exposed by the grinding. Furthermore, by performing kneading in an aqueous solution with controlled dissolved oxygen, oxidation of the alloy surface during the kneading process can be suppressed.

As a result, it becomes possible to suppress the oxide film formed on the surface of the active alloy and the elution of the alloy into the aqueous solution, and it is possible to provide a hydrogen storage alloy electrode with excellent characteristics. Furthermore, since it is an aqueous solution system, it is extremely safe and easy to implement, compared to methods that use flammable substances such as organic solvents.

(f) Example [Experiment 1 Commercially available Mm (Mitshu Metal), Ni, Co,
Each raw material of AJl is weighed to a certain composition ratio, and MmN i sCorlA J! is melted using a high-frequency melting furnace. . A hydrogen storage alloy ingot having the composition was prepared.

Next, 80 mj of water was put into a ball mill consisting of an alumina pot and a ball, and bubbling was performed with argon gas (flow rate: 6 j/M) to regulate the amount of dissolved oxygen to 5 mg71 or less. Then, 100 g of the hydrogen storage alloy ingot was added,
Ball mill pulverization was performed for about 5 hours (pulverization step).

This pulverized hydrogen storage alloy powder was thoroughly washed with water and dried in an inert atmosphere. A hydrogen storage alloy (A) according to the present invention was obtained by pulverization in this manner.

On the other hand, as a comparative example, an alloy was pulverized in the same manner as in the above example except that argon gas bubbling was not performed to obtain a comparative hydrogen storage alloy (a).

Then, the oxygen content of these invention alloys (A) and comparative alloys (B) was analyzed. The results are shown in Table 1.

From the results in Table 1, it can be seen that the alloy of the present invention (A) contains less oxygen and has a higher degree of activity than the comparative alloy (B).

[Experiment 2 In Experiment 2 below, hydrogen storage alloy electrodes were prepared and their characteristics were compared.

r Example 1) In the same manner as the alloy (A) of the present invention prepared in Experiment 1, ball milling was carried out for about 5 hours to obtain a hydrogen storage alloy powder with a particle size of 100 νm or less (pulverization step). To a slurry containing alloy powder and an aqueous solution in which the amount of dissolved oxygen was regulated to 5 mg 7'C, 1% by weight of polyethylene oxide, which has a thickening effect as a binder, was added to the alloy powder, and a slurry-like kneaded product was prepared. (kneading process). This kneaded material was pasted on both sides of a conductive core (opening rate: 50%) made of a punched metal with double/kelmettsu (the second step) and dried to obtain a hydrogen storage alloy electrode, which was designated as electrode a of the present invention. .

The electrode a of the invention thus obtained and the theoretical capacity 12
A metal-hydrogen alkaline storage battery was prepared by using a positive electrode consisting of a known sintered nickel electrode of 00+r+, Ah, a polyamide separator, and an electrolyte consisting of a KOH aqueous solution of 30 to (nominal capacity 1200mAh).

(Example 2) After boiling for 2 hours, cooling was performed to reduce the amount of dissolved oxygen to 8 mg.
80 mj/l of water was placed in a ball mill consisting of an alumina pot and balls, and then 100 g of the hydrogen storage alloy ingot prepared in Experiment 1 was added and ball milled for about 5 hours. Then, an electrode was prepared in the same manner as in Example 1, except that a slurry containing a hydrogen storage alloy powder with a particle size of 100 μm or less and an aqueous solution with a dissolved oxygen amount of 8 mg/j was used, and this was used as a battery B of the present invention. .

(Example 3) 100 g of the hydrogen storage alloy ingot produced in Experiment 1 was placed in a ball mill consisting of an alumina pot and a ball, and 0.0 g of sodium hypophosphite (hypophosphite) as a reducing agent was added.
5 g and 80 ml of water were added, and ball milling was carried out for about 5 hours. The process was carried out in the same manner as in Example 1, except that a slurry containing the hydrogen-absorbing gold powder whose particle size was reduced to 1.0 pm or less in this way and a sodium hypophosphite aqueous solution (dissolved oxygen amount = 1 mg/l) was used. A battery C of the present invention was obtained.

(Comparative example) The comparative alloy (A) prepared in Experiment 1 was used, except that water that was not bubbled with argon gas was used.
Obtain electrodes in the same manner as in Example 1, assemble a battery,
It was designated as comparative battery X.

Using the batteries A, B, C, and X produced in this way, the battery capacities were compared. The experimental conditions at this time were to charge each battery to 130% with a charging current of 0.2 C (240 mA), a discharge current of IC (1200 mA), and a final voltage of 1. This means that the battery is discharged to Ov.

The results are shown in FIG. From FIG. 1, the present invention battery A
, B, and C have an increased discharge capacity and a higher discharge voltage than comparative battery X. This is thought to be due to the fact that oxidation of the surface of the hydrogen storage alloy due to dissolved oxygen in the aqueous solution is suppressed during pulverization and kneading, and the activity is maintained at a high level.

[Experiment 3] By controlling the bubbling time of argon gas,
Comparisons were made by varying the amount of dissolved oxygen in the aqueous solution. As shown in Table 2, 6 liquids of water with different amounts of dissolved oxygen were prepared, and electrodes were manufactured in the same manner as in Example 1 to form battery cells Y and Z. It is.

Table 2 And each of these batteries was discharged in the same manner as above,
The discharge capacity of the batteries A, B, C, and X is measured.
The results are shown in Figure 2.

FIG. 2 shows the relationship between the amount of dissolved oxygen in the hydrogen storage alloy and the discharge time, that is, the discharge capacity of the battery. From this, it can be understood that by using an aqueous solution in which the amount of dissolved oxygen is 10 mg/j or less, a battery having excellent discharge capacity can be obtained.

On the other hand, if an aqueous solution with a dissolved oxygen content of 15 mg/1 or more is used, oxidation of the surface of the hydrogen storage alloy progresses and the reaction of ゛ is inhibited on the surface of the alloy, resulting in a decrease in the discharge capacity of the battery.

Although the pulverization process of the present invention was performed using a ball mill in an aqueous solution, other pulverization equipment was used and there was no temperature difference.

In addition, as a method for controlling dissolved oxygen in an aqueous solution, in addition to the above-mentioned replacement and removal by bubbling with an inert gas, methods such as reduction using a reducing agent, evaporation by boiling, etc. can be used to control dissolved oxygen. It can be regulated.

It is particularly desirable that the amount of dissolved oxygen be 10 mg/l or less.

(g) Effects of the Invention According to the method for manufacturing a hydrogen storage alloy electrode for an alkaline storage battery of the present invention, it is possible to suppress the influence of dissolved oxygen during the t-electrode manufacturing process, which deteriorates the characteristics of the hydrogen storage alloy.

As a result, the discharge capacity and i
This method can improve the t-pressure and can be easily implemented in the electrode manufacturing process, so its industrial value is extremely large.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the discharge characteristics of the battery, and FIG. 2 is a diagram showing the relationship between the amount of dissolved oxygen and the discharge capacity of the battery. A, B, C, D... Batteries of the present invention, X, Y, Z... Comparative batteries.

Claims (3)

[Claims] (1) A pulverization step of producing hydrogen storage alloy powder by pulverizing a hydrogen storage alloy lump in an aqueous solution with regulated dissolved oxygen, and kneading the hydrogen storage alloy powder and a binder in an aqueous solution with regulated dissolved oxygen. 1. A method for producing a hydrogen storage alloy electrode for an alkaline storage battery, comprising: a kneading step of obtaining a kneaded material; and a filling step of filling a conductive core with the kneaded material. (2) The method for manufacturing a hydrogen storage alloy electrode for an alkaline storage battery according to claim 1, wherein in the pulverizing step and the kneading step, the amount of dissolved oxygen in the aqueous solution is 10 mg/l or less. (3) In the pulverizing step, the particle size of the hydrogen storage alloy powder is set to 150 μm or less (
1) The method for producing the hydrogen storage alloy electrode for alkaline storage batteries.