JPH05225974A - Hydrogen storage alloy electrode - Google Patents

Abstract

PURPOSE:To lower the internal pressure of a battery with the reduction of hydrogen gas generated at the time of a charging process, and extend the service life thereof by manufacturing an electrode using hydrogen storage alloy powder available from treatment and removal of particulates with nitric acid. CONSTITUTION:Alloy powder containing approximately 15% of particulates of 10mum or less grain size is immersed in nitric acid water solution of pertinent concentration, for example, in 0.1N nitric acid at 25 deg.C for 15 minutes. Thereafter, colloidal supernatant is removed by a gradient method and, then, a product so obtained is washed, filtrated and dried, thereby obtaining hydrogen storage alloy powder. This powder contains only 1% of particulates of 10mum or less grain size, and almost all particulates initially contained are dissolved by nitric acid, or become colloidal. The colloidal particulates are separated and removed, and hydrogen storage alloy powder comprising the hydrogen storage alloy particles of 10mum or above grain size is obtained. Thereafter, this powder is used for a hydrogen storage electrode. A sealed storage battery using the electrode as a cathode electrode can restrain the internal pressure due to hydrogen gas generated at the time of charging, and the service life of the battery can be extended.

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 capable of electrochemically storing and releasing hydrogen used for a negative electrode of a secondary battery or the like.

[0002]

2. Description of the Related Art Heretofore, a nickel-hydrogen battery having a large energy density has been proposed in which an electrode using a hydrogen storage alloy is used as a negative electrode of a secondary battery, nickel oxide is used as a positive electrode, and an alkaline aqueous solution is used as an electrolytic solution. ing. In this case, the hydrogen storage alloy for the negative electrode is, for example, LaNi-based alloy, MmN.
Powders of multiple kinds of metals such as i-type alloys are weighed and mixed in a predetermined composition ratio, and the mixed powder is heated and melted by an arc melting method, and then cooled to form an ingot. It was obtained by pulverizing into a hydrogen storage alloy powder of 250 mesh or less. The hydrogen-absorbing alloy powder thus obtained is mixed with a conductive agent powder and a binder to form a mixture, and the mixture is pressed onto a porous substrate such as a nickel wire mesh to produce a hydrogen-absorbing alloy electrode. As a result, a sealed nickel-hydrogen battery is assembled.

[0003]

When the above conventional hydrogen storage alloy powder is used as the negative electrode of the above sealed nickel-hydrogen battery, hydrogen is easily generated at the time of charging, and the internal pressure increases largely at the end of charging. When the internal pressure exceeds a predetermined pressure, the safety valve is activated to discharge the gas to the outside, but if the gas is exhausted frequently, the amount of the electrolyte inside will be significantly reduced and the battery life will be shortened. ..

[0004]

DISCLOSURE OF THE INVENTION The present invention provides a hydrogen storage alloy electrode which solves the above-mentioned conventional inconvenience of a sealed nickel-hydrogen sealed battery incorporating a negative electrode manufactured by using hydrogen storage alloy powder. Then, it is manufactured by using the hydrogen storage alloy powder obtained by removing the contained fine particles with nitric acid.

[0005]

Since the hydrogen-absorbing alloy powder of the present invention has fine particles removed, a negative electrode is manufactured by using this powder, and a sealed nickel-hydrogen battery using this as a negative electrode can be charged with hydrogen even if it is charged. The gas generation is reduced, the internal pressure can be lowered, and the battery has a long life. In this case, it is general and preferable to use the hydrogen storage alloy powder from which the fine particles having a particle size of less than 10 μm have been removed, for producing the negative electrode.

[0006]

EXAMPLES Next, examples of the present invention will be described in detail. The type of hydrogen storage alloy material used in the present invention does not matter. For example, a La / Ni-based alloy in which a part of Ni of LaLi ₅ is replaced with one or more metals such as Co, Al, and Mn may be used, but from the economical viewpoint, La is a misch metal (Mm). It is desirable to use various hydrogen storage alloys replaced. Therefore, the MmNi-based hydrogen alloy powder will be described below as an example. Commercially available misch metal, nickel,
Cobalt and aluminum powders are weighed and mixed so as to have a predetermined composition ratio, for example, MmNi _4.0 Co _0.5 Al _0.5, and these are heated and melted by an arc melting method to produce a hydrogen storage alloy ingot. Then, this was mechanically pulverized to obtain a hydrogen storage alloy powder of 250 mesh or less. This alloy powder contained about 15% of fine particles having a particle size of 10 μm or less. According to the present invention, this alloy powder is diluted with an aqueous solution of nitric acid having an appropriate concentration, for example, 0.1N nitric acid
It was immersed at 5 ° C for 15 minutes. After that, the colloidal supernatant was removed by the gradient method, and then washed with water, filtered and dried to obtain the hydrogen storage alloy powder of the present invention. This alloy powder has 10
It contained only 1% of fine particles of less than μm. That is, since most of the fine particles initially contained are dissolved by the above nitric acid or become colloidal particles,
This is separated and removed to obtain a hydrogen storage alloy powder consisting of hydrogen storage alloy particles having a particle size of substantially 10 μm or more. With respect to the hydrogen storage alloy powder obtained as described above, 15 wt. % And 5 wt.% Of tetrafluoroethylene powder as a binder. %, And mixed to prepare a mixture. This mixture was pressure-bonded to a porous metal current collector plate, for example, a nickel wire mesh, by a conventional method, and a predetermined amount thereof was pressure-molded to produce a hydrogen storage alloy electrode plate of the present invention.

The hydrogen storage alloy electrode plate of the present invention is used as a negative electrode, a known paste type nickel electrode plate is used as an anode, laminated with a separator interposed therebetween, and wound into a wound electrode plate group, which is a cylindrical battery. Put in a container, inject 30% potassium hydroxide aqueous solution as an electrolytic solution, and cover the battery by a conventional method.
A cylindrical sealed nickel-hydrogen battery having a size of 1000 mAH was produced. This is hereinafter referred to as a battery of the present invention.

For comparison, the above treatment with nitric acid was not carried out, that is, 15% of the fine particles having a particle size of 10 μm or less were used.
Using the hydrogen storage alloy powder contained therein as it is, a hydrogen storage alloy electrode plate is manufactured in the same manner as above, and this is used as a negative electrode, and a wound electrode plate group is manufactured in the same manner as above, and this Was incorporated into a cylindrical battery container in the same manner as described above to prepare an AA size 1000 mAH cylindrical sealed nickel-hydrogen battery. This is hereinafter referred to as a conventional battery.

The battery of the present invention and the conventional battery were subjected to an overcharge test, and the internal pressure generated at the time of charging was measured by an internal pressure sensor mounted in advance. That is, in the overcharge test, the battery has a current of 1C (1A) and 450% of the rated capacity.
(4.5 hours) It charged and went. The internal pressure at this time was measured. As a result, the internal pressure of the battery of the present invention was 4 Kgf / cm ² , whereas the internal pressure of the conventional battery was 11 Kgf / cm ² . As is clear from the results of this comparative test, the battery of the present invention, by the above hydrogen storage alloy powder used for the negative electrode,
It was found that the rise in internal pressure during charging can be suppressed to a low level.

In the above-mentioned embodiment, the immersion treatment with nitric acid was carried out at room temperature, but the treatment time can be shortened by increasing the treatment temperature and carrying out the immersion treatment. When the hydrogen storage alloy is easily dissolved, a solution of nitric acid in which the concentration is lowered is used, or when it is difficult to dissolve, the concentration can be appropriately adjusted by increasing the concentration.

[0011]

As described above, according to the present invention, a hydrogen storage electrode is formed by using a hydrogen storage alloy powder obtained by removing fine particles contained therein, preferably particles having a particle size of less than 10 μm, with nitric acid. , The sealed battery with this as the negative electrode
The internal pressure due to the generation of hydrogen gas at the time of charging can be suppressed to a low level, which has the effect of extending the battery life.

Claims (2)

[Claims] 1. A hydrogen storage alloy electrode manufactured by using hydrogen storage alloy powder obtained by removing fine particles contained in nitric acid. 2. A hydrogen storage alloy electrode produced by using a hydrogen storage alloy powder having a content of fine particles having a particle size of less than 10 μm of 1% or less.