JPH06325761A - Manufacture of hydrogen storage electrode - Google Patents

Abstract

PURPOSE:To provide an electrode which can be simply manufactured, can obtain stable characteristics regardless of its composition, can prevent alloy powder from falling due to repeated charge/discharge, and thereby enhances its utilization factor. CONSTITUTION:The manufacture of a hydrogen storage electrode is so constituted that nickel powder is mixed with hydrogen storage alloy powder by a weight ratio of 20% to 40%, the mixture is molded with pressure, and it is then enclosed by a nickel net so as to be pressed again.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a hydrogen storage electrode which constitutes a nickel-hydride secondary battery using a hydrogen storage alloy.

[0002]

2. Description of the Related Art A nickel-hydride battery using a hydrogen-absorbing alloy has attracted attention as a high-performance secondary battery that is pollution-free and has a high energy density, and is in great demand for portable devices. As devices are made smaller and lighter, higher capacity is required for batteries used as power sources. In order to meet this requirement, the AB ₅ type hydrogen storage alloy electrode of the negative electrode has been improved by increasing the amount of lanthanum in the misch metal. In order to further increase the capacity of nickel-hydride batteries, studies have been made on AB ₂ type hydrogen storage alloys having a larger capacity than AB ₅ type hydrogen storage alloys.

AB ₅ type hydrogen storage alloy electrodes are MC, PVA
A paste-type electrode prepared by mixing a thickener such as is mainly used. On the other hand, an AB ₂ type hydrogen storage alloy electrode is generally a sintered electrode in which an alloy is pressed on a nickel net and sintered.

[0004]

The AB ₂ type alloy represented by the Laves phase hydrogen storage alloy is likely to form a passive film and has low conductivity between alloy particles, so that the initial activity is slow and the utilization rate is low. There are problems such as. Therefore, a technique for reducing the contact resistance between alloy particles is required when manufacturing an electrode using this alloy.

As a method therefor, a method of producing an electrode by sintering is generally used. However, the setting of sintering conditions differs depending on the change in alloy composition, and the process is complicated. Therefore, there has been a demand for a method for producing an electrode that can exhibit stable characteristics regardless of composition.

Further, the AB ₅ type hydrogen storage alloy electrode is required to increase its discharge capacity, and it has been improved by increasing the amount of lanthanum in the misch metal. Therefore, a technology for increasing the discharge capacity is desired.

[0007]

The present invention is characterized in that a hydrogen storage alloy is mixed with nickel powder in a weight ratio of 20% to 40%, pressure-molded, wrapped with a nickel net and pressed again. And a hydrogen storage electrode.

[0008]

The AB ₂ type hydrogen storage alloy easily forms a passive film on the surface of the alloy, and the conductivity between the alloy particles is extremely low. 20% to 4% by weight of highly conductive nickel powder as the alloy powder
By mixing 0% and press-molding, the contact resistance between alloy particles can be significantly reduced. As a result, the conductivity is improved and the utilization rate of this electrode is improved. However, only by pressure molding, the stability of the electrode is poor, and the alloy powder falls off during charge / discharge. Therefore, it is possible to prevent the alloy powder from falling off by wrapping the pressure-molded pellet with a nickel net and pressing it again and using this as an electrode.

The nickel powder mixed here has a weight ratio of 20.
% Or more and less than 40% is desirable. This is because if the nickel powder is less than 20%, the effect as a conductive agent becomes poor, and if the nickel powder is 40% or more, the capacity of the electrode as a whole decreases.

According to the present invention, stable characteristics can be obtained by the same manufacturing method regardless of the composition, and moreover, it can be easily manufactured as compared with the sintering method. This electrode manufacturing method can also be applied to an AB ₅ type hydrogen storage alloy, in which nickel powder is mixed, pressure-molded, wrapped with a nickel net and pressed again to increase the hydrogen storage capacity of the alloy.

[0011]

EXAMPLES The present invention will be described below based on examples. A hydrogen storage alloy powder sample was obtained by charging component elements weighed so as to obtain a desired composition into a crucible, melting them in a high-frequency melting furnace under an inert atmosphere, cooling and mechanically grinding or hydrogenating grinding.

The hydrogen storage alloy powder thus obtained and the nickel powder were mixed at a predetermined weight ratio, and the resulting pellet was pressure-molded with a press die to a diameter of 21 mm and a thickness of about 1 mm using a nickel net. It was wrapped and pressed again to form a hydrogen storage electrode.

In the charge / discharge test, a sintered nickel hydroxide electrode was used as the counter electrode, and an aqueous solution of potassium hydroxide having a specific gravity of 1.28 was used as the electrolytic solution. The charge was 0.1 C and 150%, and the discharge was 0.2 C and the mercury oxide electrode was used. It went to -0.6V by the standard.

Example 1 FIG. 1 shows an AB ₂ type hydrogen storage alloy containing 40% (A), 20% (B) and 0% nickel powder.
(C) is a result of conducting a discharge test on an electrode (D) which is mixed and wrapped with nickel net and pressed again, and 40% of nickel powder is mixed, and which is not wrapped with nickel net. The alloys V ₂₅ Ti ₁₇ Zr ₁₆ Ni ₄₀ Cr ₂ having the same composition were used for (A), (B), (C) and (D). About 300mA without mixing nickel powder (C)
h / g capacity, but with 20% nickel powder and 4
In (B) and (C) mixed with 0%, the capacity is 335-3.
The result was increased to 40 mAh / g. Further, in the case (D) which was not wrapped with a nickel net, the discharge capacity was decreased due to the dropping of the alloy due to repeated charging and discharging.

(Embodiment 2) FIG. 2 shows a nickel powder in an AB ₅ type hydrogen storage alloy of 40% (A), 20% (B) and 0%.
(C) is a result of conducting a discharge test on an electrode (D) which is mixed and wrapped with nickel net and pressed again, and 40% of nickel powder is mixed, and which is not wrapped with nickel net. (A), (B), (C), (D) were used alloy MmNi _3.5 Al _0.8 Co _0.7 All the same composition. 220mA without nickel powder (C)
h / g capacity, but with 20% nickel powder and 4
In (B) and (C) mixed with 0%, the capacity is 255 to 2
The result was increased to 65 mAh / g. Further, in the case (D) which was not wrapped with a nickel net, the discharge capacity was decreased due to the dropping of the alloy due to repeated charging and discharging.

In the case of both AB ₂ type and AB ₅ type alloy electrodes, nickel powder is mixed, pressure molded and wrapped with a nickel net and pressed again. The result is that the capacity is increased by about / g.

[0017]

As described above, according to the method for manufacturing a hydrogen storage electrode of the present invention, the manufacturing method is simple, stable characteristics can be obtained regardless of the composition, and the alloy powder falls off due to repeated charging and discharging. Since it is possible to provide an electrode that prevents the above-mentioned phenomenon and the utilization rate is improved, its industrial value is great.

[Brief description of drawings]

FIG. 1 is a diagram showing a change in discharge capacity when an AB ₂ type hydrogen storage alloy is used.

FIG. 2 is a diagram showing a change in discharge capacity when an AB ₅ type hydrogen storage alloy is used.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Minoru Kurohara 6-6 Josaimachi, Takatsuki City, Osaka Prefecture, Yuasa Corporation (72) Masahiko Oshiya 6-6 Josaimachi, Takatsuki City, Osaka Prefecture Inside Yuasa Corporation

Claims (1)

[Claims] 1. A method for producing a hydrogen storage electrode, comprising mixing a hydrogen storage alloy powder with a nickel powder in a weight ratio of 20% to 40%, encapsulating the pressure-molded product with a nickel net, and pressing it again.