JP2001307719A - Hydrogen storage alloy electrode - Google Patents

Abstract

(57) [Problem] To provide a hydrogen storage alloy electrode capable of reducing variation in battery capacity and high-rate discharge characteristics. SOLUTION: A band-shaped or flake-shaped hydrogen-absorbing alloy having a thickness of 20 μm or less is prepared, pulverized, formed into a paste together with a binder or a conductive material, and filled into a three-dimensional porous body or applied to a two-dimensional porous substrate. Then, a hydrogen storage alloy electrode is manufactured.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydrogen storage alloy electrode using a hydrogen storage alloy capable of reversibly electrochemically storing and releasing hydrogen.

[0002]

2. Description of the Related Art A nickel-hydrogen secondary battery has a structure in which a positive electrode mainly composed of nickel hydroxide and a negative electrode mainly composed of a hydrogen storage alloy are hermetically sealed together with an alkaline electrolyte through a separator. As the storage alloy electrode, it is common to use a hydrogen storage alloy, a binder, a conductive material, or the like, which is pasted, filled into a three-dimensional porous body, or applied to a two-dimensional porous substrate.

Usually, a hydrogen storage alloy used for a hydrogen storage alloy electrode is produced by a casting method, and is used as an electrode material by pulverizing a bulk alloy to about several tens of μm. However, the casting method has a drawback in that since the cooling capacity is low, large segregation is likely to occur, and it is difficult to form a uniform alloy structure.

As a method for solving such a problem, for example, Japanese Patent Application Laid-Open No. 7-97648 discloses a method in which a molten alloy is discharged from a pouring nozzle onto a cooled single roll or between twin rolls so as to make the molten metal uniform. A roll quenching method has been proposed in which a rapid cooling is performed to produce a ribbon-shaped or flake-shaped alloy.

[0005]

However, even if the alloy is manufactured by the roll quenching method as described above, if the thickness of the ribbon-shaped or flake-shaped alloy is large, for example, as shown in FIG. When a flake alloy 21 having a thickness of about 100 μm is produced, it is pulverized and sieved, and has an average particle size of 20 to
Even if a fine powder 22 of 30 μm is obtained, since the crystal structure of the alloy grows in the thickness direction of the flake 21, it is difficult to crack in the direction perpendicular to the thickness of the flake 21 during pulverization, The fine powder 22 having a large ratio of the major axis to the minor axis is increased because the powder 22 is easily broken.

For this reason, for example, the size of the eye is 20 to 30 μm.
When a sieve of m is used, the fine powder 22 having a long diameter larger than 20 to 30 μm is mixed with the fine powder 22 when the short diameter of the fine powder 22 passes through the mesh, and the particle size distribution is widened. As a result, there is a problem that the capacity and the high-rate discharge characteristics vary when the battery is manufactured.

The present invention has been made in view of the above-mentioned conventional problems, and has as its object to provide a hydrogen storage alloy electrode capable of suppressing variations in battery characteristics.

[0008]

The hydrogen storage alloy electrode of the present invention uses a band-shaped or flake-shaped hydrogen storage alloy having a thickness of 20 μm or less.

The hydrogen storage alloy electrode of the present invention is a strip-shaped or flake-shaped hydrogen storage alloy having a thickness of 20 μm or less, and has a ratio of the major axis to the minor axis of the pulverized alloy particles of 2.0 or less.
A hydrogen storage alloy mainly composed of the following particles is used.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a hydrogen storage alloy electrode according to one embodiment of the present invention will be described with reference to FIGS.

As shown in FIG. 1, the hydrogen storage alloy particles 1 used in the hydrogen storage alloy electrode of the present embodiment are prepared by crushing a band-shaped or flake-shaped hydrogen storage alloy 2 having a thickness of 20 μm or less and sieving it. Things.

That is, when sieving after pulverizing the hydrogen-absorbing alloy, even if the major axis of the alloy particles is large, the alloy particles pass through the mesh if the minor axis is smaller than the mesh of the sieve. Spread, which causes variations in battery characteristics. However, when the thickness of the strip-shaped or flake-shaped hydrogen storage alloy 2 is 20 μm or less, the alloy is crystal-grown in the thickness direction, so that it is hard to crack in the direction perpendicular to the thickness direction and relatively in the parallel direction. Since the alloy particles 1 are easily broken, the shape of the pulverized alloy particles 1 becomes a shape close to a cube. Therefore, since the width of the particle size distribution is narrowed, the variation in the battery characteristics can be suppressed.

In addition, after the pulverization of the strip-shaped or flaky hydrogen-absorbing alloy 2 having a thickness of 20 μm or less, if the alloy particles 1 are mainly composed of particles having a ratio of the major axis to the minor axis of 2.0 or less, the variation is particularly large. Become smaller.

Next, an example of a method for producing the hydrogen storage alloy particles 1 will be described. First, a raw material of the hydrogen storage alloy is mixed and melted, and the molten metal is rapidly cooled by a casting method such as a single roll method or a twin roll method to produce a strip-shaped or flake-shaped hydrogen storage alloy 2 having a thickness of about 20 μm or less.

An example of the twin roll method will be described with reference to FIG. 2. A melting furnace 12, a tundish 13 and a pouring nozzle 14 are disposed in an upper portion of a cooling chamber 11, and a pouring nozzle 1 is provided.
A pair of cooling rolls 15a, 15b are disposed on both sides directly below and in parallel with each other with an appropriate gap therebetween, and a molten metal 16 is supplied from a melting furnace 12 through a tundish 13 to a pouring nozzle. 14 to several hundred to several thousand r
pm, the molten metal is cooled by contacting the cooling rolls 15a, 15b on both sides, solidified while crystallizing, and cooled while flying in the cooling chamber 11 to form a flake. A hydrogen storage alloy 2 in a shape of is produced.

The thickness of the hydrogen-absorbing alloy 2 depends on the amount of molten metal jetted from the pouring nozzle 14 and the cooling rolls 15a, 15a.
b can be adjusted by adjusting the rotation speed,
In the present embodiment, the distance is adjusted to be 20 μm or less.

Thereafter, the flake-shaped hydrogen-absorbing alloy 2 is roughly pulverized and then pulverized by a wet-type bolur mill or the like to have an average particle diameter of 20 μm.
The hydrogen storage alloy particles 1 in the form of fine particles having a particle size of μm or less are pasted together with a binder, a conductive material, or the like, and filled in a three-dimensional porous body or coated on a two-dimensional porous substrate to constitute a negative electrode of a battery.

According to the nickel-hydrogen secondary battery using the negative electrode manufactured as described above, the average particle diameter of the hydrogen-absorbing alloy particles in the negative electrode is approximately 20 μm or less, and the major and minor diameters of the large particles in the hydrogen-absorbing alloy particles are smaller than 20 μm. Since the ratio is mainly 2.0 or less, the density of the active material is uniform and the variation is small, so that the variation in the battery capacity and the high-rate discharge characteristic can be reduced.

Next, specific examples will be described together with comparative examples.
You. Mm (mixture of misch metal and rare earth element), N
i, Mn, Al, and Co, each having a composition of Mm
Ni _4.1Mn_0.4Al_0.3Co_0.4Predetermined amount so that
Mix and melt by high frequency induction heating to produce molten alloy
Then, a flake-shaped hydrogen storage alloy was produced by the single roll method.
Was. At this time, the amount of molten metal injected from the injection nozzle and the roll
By controlling the number of revolutions, the thickness of the flakes becomes 15, 2
Five types of hydrogen storage alloy thin films of 0, 30, 50, and 100 μm
Pieces were made.

Each of the above alloy flakes was prepared in an Ar atmosphere at 900
Heat-treated at 1 ° C. for 1 hour. After the coarse pulverization, the powder was further pulverized by a wet ball mill. By controlling the pulverization time and the amount of zirconia balls, the average particle size was about 20 μm regardless of the type of alloy flake used. These alloy powders are designated A to E, respectively.

First, tap densities of these alloy powders A to E were measured. Sampling was performed five times and compared with the average value. As a result, in the alloy powders A (thickness 15 μm) and B (thickness 20 μm), the alloy powders C to E (thickness 30,
(50, 100 μm). This is because the alloy powders A and B are CE
It is considered that the particle shape is more uniform than that of the above.

Next, the alloy powders A to E are mixed at 90 ° C. with a specific gravity of 1.
Immersion and stirring in KOH aqueous solution for 3 hours, washing with water, dehydration,
It dried and produced the alloy powder A1-E1 for hydrogen storage alloy electrodes. For 100 parts by weight of these alloy powders, 0.15 parts by weight of carboxymethyl cellulose, 0.3 parts by weight of carbon black, 0.7 parts by weight of styrene-butadiene copolymer
A weight part was added, and water was further added thereto and kneaded to prepare a paste.

This paste was applied to a punching metal, dried, pressed to a predetermined thickness using a roll press, and cut into a predetermined size to obtain a negative electrode.

This negative electrode and a known foamed nickel type positive electrode are
It was formed into a spiral with a sulfonated polypropylene nonwoven fabric separator interposed, and inserted into a metal case. Then, an alkaline aqueous solution having a specific gravity of 1.3 containing potassium hydroxide as a main component was used as an electrolytic solution.
AA size nickel-metal hydride secondary battery A2
To E2 were prepared for each 20 cells. The capacity of each battery is 1.2A
h.

For such batteries A2 to E2, 25
The battery was activated at 10 ° C. for 15 hours at a rate of 10 hours (0.1 C) and discharged to 1 V at a rate of 5 hours (0.2 C). Then, a high-rate discharge test at 25 ° C. (charged at 0.1 C for 15 hours, and performed at a 1-hour rate (1
C), and a high-rate discharge test at 0 ° C. (charging at 25 ° C., 0.1 C for 15 hours, and discharging at 0 ° C., 1 hour rate (1 C) to 1 V).

Such a test was performed for each of 20 cells, and the variation in capacity was evaluated based on the ratio (Y) of the difference between the maximum value and the minimum value of the discharge capacity with respect to the average value of the obtained discharge capacities. The result is shown in FIG. The figure also shows the discharge capacity (activation cycle capacity) at the tenth cycle of the activation cycle.

FIG. 3 shows that when the discharge rate is low, the variation in the activation cycle capacity due to the thickness of the flake is relatively small. However, when the discharge rate is increased, when the flake thickness is 20 μm or less, the capacity variation does not change much as compared with the case where the discharge rate is low. However, when the flake thickness is 30 μm or more, the capacity variation is increased when the flake thickness is 30 μm or more. It turned out to be bigger.

[0028]

As described above, according to the present invention, since the thickness of the strip-shaped or flaky hydrogen storage alloy is 20 μm or less, the ratio of the major axis to the minor axis of the pulverized alloy particles exceeds 2.0. Particles are reduced, and therefore, when a battery is manufactured using such a hydrogen storage alloy, variations in battery capacity and high-rate discharge characteristics can be reduced.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a shape of a hydrogen storage alloy powder according to an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram of an apparatus for manufacturing a hydrogen storage alloy flake according to the embodiment.

FIG. 3 is a graph showing the relationship between the thickness of a flake for producing a hydrogen storage alloy powder and the variation in battery capacity.

FIG. 4 is an explanatory view of a shape of a conventional hydrogen storage alloy powder.

[Description of Signs] 1 Hydrogen storage alloy particles 2 Strip or flake hydrogen storage alloy

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Noriyasu Morishita 555 Sakaijuku, Kosai-shi, Shizuoka Prefecture Inside Panasonic EV Energy Corporation (72) Munehisa Ikoma 555 Sakaijuku, Kosai-shi, Shizuoka Prefecture Inside Panasonic EV Energy Corporation F term (reference) 5H050 AA08 AA19 BA14 CA03 CB17 DA03 EA10 EA22 EA28 FA17 HA04 HA05

Claims (2)

[Claims] 1. A hydrogen storage alloy electrode using a band-shaped or flake-shaped hydrogen storage alloy, wherein the hydrogen storage alloy has a thickness of 20 μm or less. 2. A hydrogen storage alloy electrode using a band-shaped or flake-shaped hydrogen storage alloy, wherein said hydrogen storage alloy has a thickness of not more than 20 μm, and a ratio of a major axis to a minor axis of crushed alloy particles is 2. A hydrogen-absorbing alloy electrode for an electrode, characterized by being mainly composed of particles having a particle size of 0 or less.