JPH04328251A - Hydrogen storage alloy electrode - Google Patents

Abstract

PURPOSE:To increase a binding force of a bored metal plate with active material mix and a collecting efficiency by letting hydrogen storage alloy powders bite the bored metal plate comprising the main component of the hydrogen storage allay powders having the active material mix applied on it. CONSTITUTION:After mixing to obtain a composition of LmNi4.0Co0.4Mn0.3 AQAl0.3, it is dissolved and cooled to be an ingot, and it is then crushed to obtain hydrogen storage allay powders of an average grain size of about 50mum. The powders are then mixed with carbon black, CMC and polyacrylic acid soda by 1, 0.5, 0.5wt.% respectively, and obtained matter is agitated while water is added for obtaining negative electrode active material paste. This paste is applied on a bored metal plate, it is dried, and a roller press is applied, so a hydrogen storage allay electrode is formed. Hydrogen storage allay can thus be let to bite the bored metal plate, the binding force of the bored metal plate with the active material mix, and the collecting efficiency can be heightened.

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.

0002

BACKGROUND OF THE INVENTION In recent years, electronic devices have become more portable and cordless due to higher integration of electronic components and advances in packaging technology. Along with this, there has been an increasing demand for higher capacity secondary batteries for driving the electronic devices.

[0003] In order to meet these demands for higher capacity, nickel-metal hydride secondary batteries that use a hydrogen storage alloy for the negative electrode have been developed with battery capacity approximately twice that of nickel-cadmium secondary batteries. .

By the way, the hydrogen storage alloy electrode incorporated in the above-mentioned nickel-metal hydride secondary battery etc. is usually manufactured as follows. First, a hydrogen storage alloy ingot is pulverized by a hydrogen gas pulverization method or a mechanical pulverization method to produce a hydrogen storage alloy powder, or a molten alloy is sprayed by a gas atomization method to produce a spherical hydrogen storage alloy powder. Next, an active material paste containing the hydrogen storage alloy powder as a main component is prepared. After applying this active material paste to the conductive core, it is dried, pressed, and cut. In this way, a hydrogen storage alloy electrode is manufactured by coating the conductive core with an active material mixture containing hydrogen storage alloy powder as a main component.

[0005] The conductive core used in the above-mentioned hydrogen storage alloy electrode includes, for example, a perforated metal plate typified by punched metal, or typified by metal net or foamed metal such as Celmet (trade name manufactured by Sumitomo Electric Industries, Ltd.). Examples include three-dimensional metal porous bodies. However, the conductive core made of the three-dimensional metal porous body is expensive due to its complicated manufacturing process, and has poor mechanical strength, which limits the amount of active material paste that can be filled and increases the density of the hydrogen storage alloy of the electrode. The problem is that it is difficult to increase the

On the other hand, the perforated metal plate has the advantage of being inexpensive and having excellent mechanical strength because it has a simple structure in which many openings with a diameter of several mm are formed in a smooth metal plate. For this reason, various hydrogen storage alloy electrodes using perforated metal plates as conductive cores have been studied.

However, in the hydrogen storage alloy electrode using the perforated metal plate, although the active material mixture is applied and pressed onto the surface of the perforated metal plate, the active material mixture easily falls off and further collects. Due to poor power efficiency, there was a problem in that the battery voltage decreased during large current discharge.

[0008] In order to increase the binding force between the perforated metal plate and the active material mixture and to improve the current collection efficiency of the electrode, the surface of the perforated metal plate may be physically roughened by sandblasting or the like, or treated with chemicals. Attempts have been made to chemically roughen the active material paste, or to mix a large amount of a binder into the active material paste. However, these attempts have not resulted in a fundamental solution due to problems such as an increase in the number of steps, complicating manufacturing, and deterioration of battery characteristics.

[0009]

[Problems to be Solved by the Invention] The present invention has been made in order to solve the problems of the prior art, and it provides a hydrogen hydride solution that increases the bonding force between the perforated metal plate and the active material mixture, and improves the current collection efficiency. The present invention aims to provide a storage alloy electrode.

0010

[Means for Solving the Problems] The present invention provides a hydrogen storage alloy electrode in which a perforated metal plate is coated with an active material mixture containing hydrogen storage alloy powder as a main component. This is a hydrogen-absorbing alloy electrode characterized by a wedge-shaped structure. Examples of the perforated metal plate include punched metal and nickel-plated punched metal. Examples of the active material mixture include those having a composition in which hydrogen storage alloy powder is mixed with conductive material powder and a binder.

[0011] The hydrogen storage alloy is not particularly limited, and any metal may be used as long as it can store hydrogen electrochemically generated in the electrolyte and can easily release the stored hydrogen during discharge. . For example, general formula XY5-a
Za (however, X is a rare earth element including La, Y is Ni, Z
is Co, Mn, Al, Fe, Ti, Cu, Zn, Zr,
At least one element selected from Cr, V, and B (a represents 0≦a<2.0) is used. Specifically, LaNi5, MmNi5, LmNi5 (
Lm; lanthanum-enriched misch metal), and some of these Nis are converted into Co, Mn, Al, Fe, Ti, Cu,
Examples include multi-element materials substituted with elements such as Zn, Zr, Cr, V, and B.

[0012] Examples of the conductive material powder include carbon black, graphite, and acetylene black. The blending ratio of the conductive material powder is preferably in the range of 0.1 to 4 parts by weight per 100 parts by weight of the hydrogen storage alloy powder. A more preferable blending ratio of the conductive powder is 0.1 to 2 parts by weight per 100 parts by weight of the hydrogen storage alloy powder.
Parts by weight range.

Examples of the binder include polyacrylates such as sodium polyacrylate and potassium polyacrylate, fluororesins such as polytetrafluoroethylene (PTFE), and carboxymethyl cellulose (CM
C) etc. The blending ratio of the binder is 0.1 to 5 parts by weight per 100 parts by weight of the hydrogen storage alloy powder.
It is desirable that the amount be in the range of parts by weight.

[0014] It is desirable that the area ratio in which the hydrogen storage alloy powder bites into the surface of the perforated metal plate (excluding the openings) is 20% or more. As the hydrogen storage alloy powder, from the viewpoint of making it easy to bite into the perforated metal plate and sufficiently improving the binding force between the perforated metal plate and the active material mixture,
It is desirable that the surface has ridge lines, that is, a shape with corners. Hydrogen storage alloy powder with such a shape is
For example, it can be produced by crushing an ingot of a hydrogen storage alloy.

The hydrogen storage alloy electrode described above is manufactured, for example, as follows. First, an active material paste containing the hydrogen storage alloy powder as a main component is prepared. Subsequently, this active material paste is applied to the perforated metal plate, dried, and then rolled and pressed to produce a hydrogen storage alloy electrode. In manufacturing such a hydrogen storage alloy electrode, in order to make the hydrogen storage alloy powder bite into the perforated metal plate, the hydrogen storage alloy powder is applied to the perforated metal plate coated with the active material mixture using a rolling press process or an independent process, for example. Just apply enough pressure to make the powder bite.

[0016]

[Operation] According to the present invention, in a hydrogen storage alloy electrode in which a perforated metal plate is coated with an active material mixture containing hydrogen storage alloy powder as a main component, the hydrogen storage alloy powder is bitten into the perforated metal plate. This increases the binding force between the perforated metal plate and the active material mixture, and improves the conductivity between the punched metal and the active material mixture, thereby increasing current collection efficiency. As a result, it is possible to prevent the active material mixture from falling off, and to improve battery characteristics.
In particular, a hydrogen storage alloy electrode with improved large current discharge characteristics can be obtained.

[0017]

EXAMPLES Examples of the present invention will be described in detail below. Examples 1 and 2 and comparative examples 1 and 2

First, lanthanum-enriched misch metal (Lm
), nickel, cobalt, manganese, and aluminum with a composition of LmNi4.0 Co0.4 Mn0.3 Al0
．． After weighing and mixing so as to give a hydrogen storage alloy ingot of 3, the mixture was melted and cooled in a high frequency induction furnace to produce a hydrogen storage alloy ingot. Subsequently, this ingot was heat treated in an electric furnace and then ground in a hammer mill to obtain a hydrogen storage alloy powder having ridge lines on the surface and having an average particle size of about 50 μm. This hydrogen storage alloy powder contains 1% by weight of carbon black and 0.5% by weight of CMC.
, and 0.5% by weight of sodium polyacrylate were mixed, and then water was added with stirring until it became paste-like to prepare a negative electrode active material paste. Subsequently, this negative electrode active material paste was applied to a punched metal (made of mild steel) with a thickness of 80 μm.
The surface was coated with nickel plating with a thickness of 3 μm) and dried to obtain an active material mixture coated plate with a width of 5 cm.

[0019] Next, roller pressing was performed three times in which the active material mixture coated plate was passed between opposing rollers having a diameter of 150 mm. In each of the roller presses, four types of hydrogen storage alloy electrodes were produced by changing the roller spacing to adjust the pressure applied to the active material mixture coated plate as shown in Table 1 below. Examples 3 and 4

First, the composition is LmNi4.0 Co0.4
A spherical hydrogen storage alloy powder (average particle size: about 50 μm) with a smooth surface was produced by gas atomization using Mn0.3 Al0.3. A hydrogen storage alloy electrode was produced using this hydrogen storage alloy powder under the same conditions as in Examples 1 and 2.

The obtained hydrogen storage alloy electrodes of Examples 1 to 4 and Comparative Examples 1 and 2 were impregnated with epoxy resin and cured, and then cut and the cross section was observed with a microscope to determine the hydrogen absorption into the punched metal. The degree of penetration of the storage alloy powder was investigated. The results are also listed in Table 1 below.

[0022] For the hydrogen storage alloy electrodes of Examples 1 to 4 and Comparative Examples 1 and 2, adhesive tape was attached to the electrode surface, and then the adhesive tape was applied at a rate of 1 cm/sec in a direction perpendicular to the electrode surface. Peel off at speed and remove 1cm of adhesive tape.
A peel test was conducted to measure the amount of active material mixture attached to each piece. The results are also listed in Table 1 below.

Furthermore, the hydrogen storage alloy electrodes of Examples 1 to 4 and Comparative Examples 1 and 2 were each wound together with a nickel electrode through a nylon separator to assemble an AA size nickel-metal hydride secondary battery. The obtained batteries were charged at 1/3 CmA and then discharged at 3 A, and a large current discharge characteristic test was conducted to determine the average discharge voltage. The results are also listed in Table 1.

[0024]

[Table 1]

As is clear from Table 1, the electrodes of Examples 1 to 4 have a smaller amount of active material mixture peeled off than the electrodes of Comparative Examples 1 and 2, and when incorporated into a battery, the electrodes have a large current discharge. It can be seen that the average discharge voltage at the time is high. This is due to the hydrogen storage alloy powder biting into the surface of the punched metal, which increases the binding strength between the punched metal and the active material mixture, and the electrical conductivity between the punched metal and the active material mixture. This is due to the improved current collection efficiency.

Although the electrode of Example 1 was produced by roller pressing at the same pressure as the electrode of Example 3, the amount of active material peeled off was large due to the large penetration of the hydrogen storage alloy powder into the punched metal. It can be seen that the average discharge voltage during large current discharge is high when the battery is small and incorporated into a battery. On the other hand, although the electrode of Example 2 was produced by roller pressing at the same pressure as the electrode of Example 4, the amount of exfoliation of the active material was small because the hydrogen storage alloy powder penetrated into the punched metal to a large extent. It can be seen that when incorporated into a battery, the average discharge voltage during large current discharge is high. These problems are caused by the fact that the hydrogen storage alloy powder has a shape with ridge lines on its surface, so it easily bites into the punched metal. In addition,
Although the roller press was performed three times in the above embodiment, it is possible to perform the roller press only once by increasing the pressure.

In addition, in the above embodiment, the hydrogen storage alloy powder was bitten into the punched metal by the pressure applied by the roller press, but the hydrogen storage alloy powder was bitten into the punched metal by the pressure applied in a process other than the roller press. Similar results can be obtained even if

[0028]

[Effects of the Invention] As detailed above, it is possible to increase the binding force between the perforated metal plate and the active material mixture, and to improve the conductivity between the punched metal and the active material mixture, thereby increasing the current collection efficiency. As a result, it is possible to prevent the active material mixture from falling off, and to provide a hydrogen storage alloy electrode that has improved battery characteristics, particularly large current discharge characteristics.

Claims (1)

[Claims] [Claim 1] A hydrogen storage alloy electrode in which a perforated metal plate is coated with an active material mixture containing hydrogen storage alloy powder as a main component, characterized in that the hydrogen storage alloy powder is bitten into the perforated metal plate. Hydrogen storage alloy electrode.