JPS6077357A - Electrode which can absorb hydrogen - Google Patents

Abstract

PURPOSE:To increase the mechanical strength and the charge-and-discharge cycle life of an electrode which can absorb hydrogen by preventing any separation of the hydrogen-absorbing material from the surface of the electrode and preventing any cracks from developing in the electrode. CONSTITUTION:After titanium of at least 99.5% purity and nickel are weighed in an atomic ratio of 2:1, the mixture is heated and molten in an argon atmosphere in an arc melting furnace to produce a Ti2Ni alloy. An alloy powder 4 obtained by pulverizing this alloy principally consists of the Ti2Ni phase and contains the TiNi phase, the TiNi3 phase and simple metals of the Ti phase and the Ni phase. The alloy powder 4 is packed into a foamy metal 3 made of nickel before pressing is performed, then the pressed body is sintered in vacuum at 920 deg.C for one hour thereby making a sintered electrode. After that, sputter vapordeposition is performed on both surfaces of the plate body of the sintered electrode by using a sputter device until the sintered electrode is coated with thin nickel films 2 of 1,000Angstrom thickness, thereby obtaining an electrode which can absorb hydrogen. In addition to nickel, electrolyte resistant metals such as a stainless steel can be used as a material used to form thin metallic vapordeposition films.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to improvements in hydrogen storage electrodes used, for example, as cathodes of alkaline storage batteries.

Conventional Structure and Problems The hydrogen storage electrode has a structure in which a hydrogen storage material is held inside a metal porous material such as nickel having a three-dimensional network structure, so-called foamed metal.

Generally, electrodes using foamed metal (hereinafter referred to as foamed metal) are made by filling a three-dimensional mesh with hydrogen storage material powder or a mixed powder of a single metal that forms a hydrogen storage alloy and press-forming it. Manufactured by heat treatment at sintering or alloying temperatures.

However, even if a relatively strong electrode is manufactured by filling a foamed metal with a hydrogen absorbing material, the hydrogen absorbing material will repeatedly expand and contract as it repeatedly absorbs and releases hydrogen in the electrolyte. , the bonding force between the electrode constituent materials weakens, and the hydrogen storage material gradually begins to fall off from the electrode surface, causing a decrease in capacity. Further, due to the heat treatment during electrode production, the foamed metal may react with the hydrogen storage material or a part of the single metal, and one foamed metal may become alloyed. As a result, the foamed metal loses its original skeletal strength and becomes brittle, and repeated charging and discharging can cause cracks in the electrodes. In addition, some of the alloys formed by the metal foam form hydrogen storage materials. In such a case, a portion of the electrode support repeatedly absorbs and releases hydrogen due to charging and discharging, and the strength of the electrode further decreases. For example, titanium 12 is used as a hydrogen storage material.

When using a Kel-based alloy, if the material of the foam metal is nickel, some alloys that form metal hydrides such as T 12Ni and TiNi will be formed, and the strength of the electrode will further decrease due to charging and discharging. ((In order to solve the above problems, for example, Japanese Patent Application Laid-Open No. 53-32349
The publication proposes coating the surface of the hydrogen storage electrode with a porous sintered nickel layer. However, the thickness of this porous nickel layer is 0.6 to 3 mm, and the capacity per unit weight (Ah/f) or the capacity per unit volume (Ah
/cc) becomes smaller.

Purpose of the Invention The present invention eliminates these conventional problems, and provides a hydrogen storage material that does not cause the hydrogen storage material to fall off, prevents cracks in the electrodes and decreases in strength, and can be charged and discharged for a long period of time. It provides electrodes.

Structure of the Invention The present invention uses vapor deposition to form a metal thin film on the surface of a hydrogen storage electrode in which a foamed metal is filled with a hydrogen storage material.Charging and discharging prevents the hydrogen storage material in the foamed metal from falling off and the electrode itself. Prevents capacity loss and cycle life reduction due to cracks, strength loss, etc.

DESCRIPTION OF EMBODIMENTS The present invention will now be described by way of embodiments. Commercially available purity 9
9.5% or more of titanium and nickel were weighed to have an atomic ratio of 2:1K, and heated and melted in an argon atmosphere in an arc melting furnace to obtain a Ti2Ni alloy. This alloy was pulverized to obtain alloy powder of 37 μm (30 meshes) or less. The obtained alloy powder mainly consists of a T 12 N i phase, and also consists of a T1Ni phase, a TiNi3 phase, and single metals of a Ti phase and a Ni phase.

This alloy powder is applied to a foamed metal (30 mm) made of nickel.
x 30 order) and pressed at 1,8 ton/ci, in vacuum (10'-' to 10-' Torr)
Sintering was performed at a temperature of 920° C. for about 1 hour to obtain a sintered electrode.

Next, a thin nickel film was sputter-deposited on both sides of the plate-shaped sintered electrode using a sputtering device so that the thickness of the nickel film was 10 mm, and both sides of the electrode were coated with the thin nickel film to a thickness of 0 mm. A hydrogen storage electrode of 95+++ m was obtained. This electrode is A
For comparison, an electrode not coated with a nickel thin film is designated as B. The electrode of this example is shown in FIG. 1, in which a is a front view, b is a bottom view, and C is a side view.

In FIG. 1, the electrode of the present invention has a nickel thin film 2 formed by vapor deposition on the surface of a foamed metal 3 containing a hydrogen storage material 4, and a lead terminal 1 fixed to the foamed metal 3.

An alkaline storage battery was constructed using these electrodes as cathodes and a known nickel electrode as an anode. Charging is done using hydrogen storage material 17
The discharge was carried out at 950 mA for 17 cycles. Figure 2 shows the change in discharge capacity when charging and discharging were repeated. The discharge was performed at a cathode potential of -700% V-J with respect to the mercury oxide electrode, and the initial life was 1 to 5.
The time point was defined as the point when the capacitance of the cycle decreased to Z or less. The discharge capacity was expressed as a value per unit weight of the hydrogen storage material of the cathode.

As shown in Fig. 2, by covering both sides of the plate-like body of the hydrogen storage electrode, which is a foam metal filled with hydrogen storage A2, with a nickel thin film, the initial discharge capacity is lower than that of B.
The number of charge/discharge cycles is more than twice that of B. That is, in B, the hydrogen storage material expanded and contracted repeatedly due to repeated charging and discharging, and the bond between the electrode constituent materials became weaker, and it was observed that they fell off from the electrode surface. Furthermore, the foamed metal of the support formed an alloy with the hydrogen storage material, reducing its strength and causing a crack in the center of the electrode.

In contrast, in the electrode A of the present invention, both surfaces of the electrode are coated with a nickel thin film, so that the hydrogen storage material does not fall off and the electrode does not crack. Therefore, it can be charged for more than 400 cycles.
Even after repeated discharges, almost no decrease in capacity was observed, showing good characteristics.

A sintered electrode was made in the same manner as in the above example, and hydrogen storage electrodes with Niskel thin films of different thicknesses were made using a sputtering device, and an alkaline storage battery was constructed in the same manner and a charge/discharge test was conducted. The results are shown in the table below.

In the eight types of electrodes shown in the margin table below, it was found that the thickness of the nickel thin film for electrodes (1) and (2) had almost no coating effect. This is because the thickness of the nickel thin film is very thin, and as in the case where no metal thin film is covered, cracks occur in the electrode due to repeated charging and discharging, and the active material falls off from the cracks. The effect appears from electrode (1), and there is almost no change in electrodes (2) to (2) after 400 cycles, indicating that the nickel thin film has an effect. Therefore, the thickness of the nickel thin film is 60
Approximately 0 to 2,000 people are suitable; if it is thinner than that, the effect will be small, and if it is thicker than that, the discharge capacity density will be small. Since the vapor deposition is a thin film, the capacity per unit weight (Ah/
! i') or capacity per unit volume (Ah/cc)
There is almost no decrease in the amount of electricity, and a utility pole with high capacity and long life can be obtained.

Materials that are resistant to corrosion in alkaline electrolytes, such as, can be applied.

Effects of the Invention As described above, the present invention eliminates the dropping of the hydrogen storage phase from the electrode surface and the cracking of the electrode by coating the surface of the hydrogen storage electrode, which is a foamed metal filled with a hydrogen storage material, with a vapor-deposited metal thin film. , a hydrogen storage electrode with excellent mechanical strength and a good charge/discharge cycle life is obtained.

[Brief explanation of the drawing]

The first view of the electrode area, and Figure 2 shows the electrode area using a hydrogen storage electrode.
＼ It is a diagram showing changes in discharge capacity due to charging and discharging of a lucali storage battery. 2-nickel thin film, 3...foamed metal, 4...hydrogen storage material. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure ((L) (b) (C) Figure 2 Light release cycle number

Claims (1)

[Claims] A hydrogen storage electrode characterized in that the surface of a foamed metal filled with a hydrogen storage material is coated with a vapor-deposited metal thin film.