JPH053031A - Manufacture of alkaline storage battery and its negative electrode - Google Patents

Abstract

PURPOSE:To provide a battery having excellent charging characteristics and high efficiency discharging characteristics by improving hydrogen storage alloy powders in an alkaline battery, the negative electrode of which being made of the hydrogen storage alloy powders. CONSTITUTION:Hydrogen storage alloy powders, the shape of which being spherical and the surface contour of which being irregular, are used. Whereby, hydrogen storage powders, in which the diffusion velocity of hydrogen being fast and the specific surface area of which being large, can be provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an alkaline storage battery and its negative electrode, and more particularly to an alkaline storage battery using a hydrogen storage alloy capable of electrochemically storing and releasing hydrogen, which is the active material of the negative electrode, and its negative electrode. It relates to a manufacturing method.

[0002]

2. Description of the Related Art Hydrogen storage alloys that store and release a large amount of hydrogen have attracted attention as electrode materials having high energy density and are being applied to alkaline storage batteries aiming at high capacity.

The hydrogen storage alloy is used as a negative electrode of an alkaline storage battery by making an alloy lump into a fine powder having an appropriate particle size and coating it as a paste on a porous steel plate or filling a three-dimensional substrate such as a foam metal substrate. . In order to obtain this fine powder, it is general to pulverize mechanically or by repeating occlusion / release of hydrogen gas. Here, it is clear that the particle size of the fine powder means the diffusion distance of the stored hydrogen. Therefore, the charging characteristics of this battery are improved by selecting an appropriate particle size.

[0004]

However, since the powder thus obtained is in the form of fine fragments by the above-mentioned pulverization, the diffusion distance of hydrogen from the surface of the powder to the inside is not constant, so that the hydrogen diffusion is unsatisfactory. Be uniform. Therefore, when charging at a high rate, the hydrogen diffusion in the alloy becomes rate-determining, and it is not possible to charge only the amount of electricity that has flowed for charging. That is, there is a problem that the charging efficiency is reduced. Therefore, by using a spherical hydrogen storage alloy powder, the diffusion distance of hydrogen becomes constant from any point on the powder surface, uniform diffusion is possible, and a battery having excellent filling characteristics can be obtained. This spherical powder is atomized by compressed gas or liquid of molten alloy (atomize)
In this method, the process from melting the alloy to obtaining the powder is one step, and therefore simplification of the step can be expected.

However, if only the powder having a spherical shape is used, the specific surface area of the alloy powder becomes the minimum value, and when it is used as an electrode, the contact area between the surface of the hydrogen storage alloy and the electrolytic solution decreases, and the current density increases. Therefore, the polarization of the negative electrode becomes large especially at the time of high-rate discharge, the battery voltage decreases, and the battery capacity decreases, so that the advantages of the high-capacity alkaline storage battery are lost.

The present invention solves such problems, and an object of the present invention is to provide an alkaline storage battery excellent in charge characteristics without deteriorating discharge characteristics and a method for manufacturing the negative electrode thereof.

[0007]

In order to solve these problems, the method for producing an alkaline storage battery and its negative electrode of the present invention uses a hydrogen storage alloy powder having a spherical powder shape and an uneven surface shape. And constitutes an alkaline storage battery.

[0008]

With this structure, in the method of manufacturing the alkaline storage battery and the negative electrode thereof of the present invention, the hydrogen diffusion rate is improved by using the hydrogen storage alloy powder, which has a spherical powder shape and an uneven surface shape, for the negative electrode. It will be.

That is, by using a hydrogen storage alloy having a spherical powder shape and an uneven surface shape, the rate of hydrogen diffusion is increased, the charging efficiency is improved, and the current density during high-rate discharge is increased. It is possible to prevent a significant increase in the discharge voltage and a decrease in the discharge voltage.

Further, after the molten metal of the hydrogen storage alloy is atomized to obtain the hydrogen storage alloy powder, the hydrogen storage alloy powder is dipped in an alkaline aqueous solution to have a spherical shape and an uneven surface shape. It is possible to easily obtain the hydrogen storage alloy powder shown and to provide a hydrogen storage alloy negative electrode having excellent charge and discharge characteristics.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method of manufacturing an alkaline storage battery and its negative electrode according to an embodiment of the present invention will be described in detail below with reference to the drawings. The charging efficiency was measured using a model battery with negative electrode capacity regulation.
The high rate discharge characteristics are measured with a battery having a regulated positive electrode capacity.

A hydrogen storage alloy that electrochemically stores and releases hydrogen, which is an active material, and its electrode were prepared by the following method.

Cerium about 40 wt%, lanthanum about 30 w
The atomic ratio of misch metal (hereinafter referred to as Mm) containing t% and about 13 wt% of neodymium as main components, nickel, cobalt, aluminum and manganese is 1: 3.5.
Weigh to be 5: 0.75: 0.3: 0.4.
This was melted in a high frequency melting furnace to prepare a hydrogen storage alloy of MmNi _3.55 Mn _0.4 Al _0.3 Co _0.75 having a CaCu ₅ type crystal structure. This was melted again at 1180 ° C. and sprayed with a high-pressure argon gas to obtain a spherical hydrogen storage alloy powder 1 having an average particle diameter of 25 μm shown in FIG. Hydrogen storage alloy powder 1 with a specific gravity of 1.30 and KO of 80 ° C
It was dipped in an aqueous solution of H and subjected to surface etching, and the uneven surface was used as the uneven surface 2 containing a large amount of Ni as compared with the internal alloy composition. Then, a 1 wt% aqueous solution of carboxymethyl cellulose was added thereto to form a paste, and the thickness was 0.9.
It was filled in a sponge-like nickel porous body which was a support having a porosity of about 95%. This was dried at 100 ° C. and then pressed to form an electrode plate having an average thickness of 0.5 mm. Then, this was cut into a width of 20 mm and a length of 20 mm, and the charge / discharge capacity was 200 mAh.
The negative electrode 3 of the hydrogen storage alloy electrode of was obtained. This was sandwiched by a positive electrode 5 having a sufficiently large capacity via a polyamide nonwoven fabric separator 4 and immersed in an electrolyte solution 6 of a 7.1 N KOH aqueous solution to form a model battery as shown in FIG.

The electrode plate has a width of 39 mm and a length of 80 mm.
After cutting into pieces, a hydrogen storage alloy electrode having a chargeable / dischargeable capacity of 1600 mAh was obtained. The hydrogen storage alloy electrode thus obtained was used as a negative electrode, and an electrode group was constituted by a known foam metal nickel positive electrode having a capacity of 1000 mAh and a sulfonated polypropylene nonwoven fabric separator obtained by sulfonating a polypropylene nonwoven fabric. Then, after injecting 2.2 cm ^{3 of} 7.1N KOH aqueous solution, it was sealed and a battery A of AA (R6) size was manufactured.

As a comparative example, the hydrogen-absorbing alloy powder 1a shown in FIG. 2 which is not subjected to surface etching and has a spherical shape and a spherical shape, and the alloy prepared in a high frequency melting furnace were mechanically pulverized to obtain the powder. Using the fragmentary hydrogen storage alloy powder 1b having an average particle diameter of 25 μm shown in FIG. 3, a model battery similar to that of FIG. 4, and AA size batteries B and C were prepared.

The model battery was charged at 200 mA for 1 hour in an atmosphere of 20 ° C. and discharged at 20 mA, and the ratio of the discharge capacity to the amount of charged electricity was measured.

The discharge characteristics are as follows: AA size battery was initially charged at 100 mA for 15 hours in an atmosphere of 20 ° C.,
It was discharged to 1.0 V at 200 mA. After that, these batteries were charged under the same conditions as above, discharged at a constant current of 3000 mA, and the discharge capacity up to 1.0 V was measured.

The measurement was carried out for each of the five batteries and the average was taken. (Table 1) shows the number of each battery, the shape of the powder, and the battery characteristics.
Moreover, the average discharge curve at the time of high rate discharge is shown in FIG.

[0019]

[Table 1]

As a result, in the batteries A and B, since the hydrogen storage alloy having a spherical powder shape was used as the negative electrode, hydrogen diffusion was fast and high charging efficiency was exhibited. In addition, since the battery A uses the hydrogen storage alloy powder 1 having irregularities on the surface, the high rate discharge characteristics are also good. However, while high-rate charging limits the rate of hydrogen diffusion inside the hydrogen-absorbing alloy powder, high-rate discharge characteristics are greatly affected by the area where the powder surface contacts the electrolyte and the current density. The battery B using the hydrogen-absorbing alloy powder 1a having no unevenness is a battery C using the hydrogen-absorbing alloy powder 1b whose discharge capacity at high rate discharge is fragmentary.
More significantly lower. This is because the hydrogen storage alloy powder 1a used in the battery B has a spherical shape with no unevenness on the surface, and therefore the specific surface area of the powder is minimized. For example, when the BET method is used for measurement,
It is about 0.03 m ² / g, which is smaller than the fragmentary hydrogen-absorbing alloy powder 1b (about 0.2 m ² / g) used in the battery C, and at a large current of 3000 mA as shown in FIG. When the high-rate discharge is performed, the voltage drop is large, and the discharge capacity is remarkably reduced in the capacity until the battery voltage 1.0V which is usually used is reached. However, as is clear from the result of the battery A, by making the surface shape of the spherical hydrogen storage alloy powder 1 uneven, the specific surface area can be dramatically increased (about 0.6 m ² / g). Thus, a battery having excellent discharge characteristics was obtained. In addition, it is considered that in the spherical powder 1a as shown in FIG. 2 in which the surface is not uneven, the contact point between the powders and the contact point between the powder and the current collector becomes small, which causes the deterioration of the battery characteristics. It is considered that the hydrogen storage alloy powder 1 shown in FIG. 1 has a good surface contact between the powders and the contact between the powders and the current collector, which contributes to the improvement of the high rate discharge characteristics. .

[0021]

As is apparent from the above description of the embodiments, according to the method for manufacturing an alkaline storage battery and its negative electrode of the present invention, a hydrogen storage alloy having a spherical shape and a surface shape having irregularities was used. As a result, there is an effect that it is possible to provide an alkaline storage battery having high charging efficiency even at a high rate of charging and having excellent discharge characteristics even when discharged at a large current.

[0024] Further, there is an effect that it is possible to provide an alkaline storage battery having excellent charging characteristics and discharging characteristics by atomizing the molten metal of the hydrogen storage alloy and then immersing it in an alkaline aqueous solution.

[Brief description of drawings]

FIG. 1 is a sectional view schematically showing a hydrogen storage alloy powder having a spherical shape and an uneven surface shape in a method for producing an alkaline storage battery and a negative electrode thereof according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view schematically showing a hydrogen storage alloy powder having a spherical shape and a surface having no unevenness in a comparative example.

FIG. 3 is a cross-sectional view schematically showing the fragmentary hydrogen storage alloy powder.

FIG. 4 is a conceptual diagram showing the configuration of a model battery for measuring the charging efficiency in the method of manufacturing an alkaline storage battery and its negative electrode according to one embodiment or comparative example of the present invention.

FIG. 5 is a graph showing average discharge characteristics of batteries using the respective powders.

[Explanation of symbols]

1 Hydrogen storage alloy powder 2 Uneven surface with a lot of Ni 3 Negative electrode 4 positive electrode 5 separator 6 Electrolyte

Continued front page    (72) Inventor Isao Matsumoto             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd.

Claims (4)

[Claims] 1. A positive electrode mainly composed of a metal oxide, a negative electrode mainly composed of a hydrogen storage alloy powder capable of electrochemically storing and releasing hydrogen as an active material, a separator, and an alkali. An alkaline storage battery mainly composed of an electrolytic solution, wherein the hydrogen storage alloy powder has a spherical shape. 2. The alkaline storage battery according to claim 1, wherein the surface shape of the spherical hydrogen storage alloy powder is uneven. 3. The alkaline storage battery according to claim 2, wherein the surface composition of the hydrogen storage alloy having irregularities has a higher Ni content than the internal alloy composition. 4. A step of obtaining a hydrogen storage alloy powder by spraying a molten metal of the hydrogen storage alloy in a negative electrode for an alkaline storage battery containing a hydrogen storage alloy as a main constituent material, and immersing the hydrogen storage alloy powder in an alkaline aqueous solution. The manufacturing method of the negative electrode for alkaline storage batteries which has a process.