JPH05343059A - Hydrogen storage alloy electrode - Google Patents

Abstract

PURPOSE:To provide a hydrogen storage alloy electrode whose initial characteristic is improved by covering the surface of hydrogen storage alloy used in an electrode with alkali - soluble metal or the oxide. CONSTITUTION:The surface of hydrogen storage alloy powder to store or release hydrogen reversibly is covered with alkali soluble metal such as Al or the oxide such as Al2O3. This covering can be carried out by a mechanical alloying treatement. An electrode is molded by using this covered alloy powder. When this electrode is molded, this alloy is prevented from being oxidized due to the covering. When this electrode is incorporated into a battery, the covering is dissolved by alkaline electrolyte, and a reacted surface is exposed on the alloy surface. In the hydrogen storage alloy electrode obtained in this way, since a charge and discharge reaction makes progress speedily on the alloy surface from the initial stage of a cycle, an initial characteristic can be improved.

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 used in a metal-hydrogen alkaline storage battery.

[0002]

2. Description of the Related Art Conventionally used storage batteries include alkaline storage batteries such as nickel-cadmium storage batteries and lead storage batteries. However, in recent years, it has been possible to provide a hydrogen storage alloy that reversibly stores and releases hydrogen, which is the negative electrode active material, especially under normal pressure because it is lighter in weight and has a higher capacity than these storage batteries. Attention has been paid to a metal-hydrogen alkaline storage battery in which an electrode is used as a negative electrode and an electrode having a metal oxide such as nickel hydroxide as a positive electrode active material is used as a positive electrode. The charging / discharging reaction at the hydrogen storage alloy electrode of this battery is represented by Chemical formula 1.

[0003]

[Chemical 1]

[In the above formula, M represents a hydrogen storage alloy, and MH represents a hydrogen storage alloy in which hydrogen is stored. ] That is,
Charging is performed by an occlusion reaction in which water molecules in the electrolytic solution become hydrogen atoms on the surface of the alloy and are occluded in the alloy. On the other hand, the discharge is performed by a release reaction in which the hydrogen storage alloy electrochemically releases hydrogen. And this release reaction is
The atomic hydrogen stored inside the electrode proceeds by reacting with OH ⁻ existing around the hydrogen storage alloy.

[0005]

However, in the battery using the above hydrogen storage alloy, the hydrogen storage alloy easily reacts with oxygen in the air during the battery manufacturing process, so that an oxide film exists on the surface of the alloy. Become. As a result, the charge / discharge reaction on the surface of the alloy is hindered, so that there is a problem that the initial characteristics are deteriorated.

The present invention has been made in view of the above problems, and an object thereof is to provide a hydrogen storage alloy electrode capable of improving initial characteristics.

[0007]

In order to solve the above problems, the present invention provides a hydrogen storage alloy electrode containing a hydrogen storage alloy capable of reversibly storing and releasing hydrogen, wherein the alloy surface has:
It is characterized in that it is coated with an alkali-soluble metal or its oxide.

[0008]

In the battery having the hydrogen storage alloy electrode whose surface is coated with the alkali-soluble metal (or metal oxide) as described above, the hydrogen storage alloy is oxidized by oxygen in the air during the battery manufacturing process. Never. On the other hand, after the battery is manufactured, the alkali-soluble metal (or metal oxide) is dissolved by the alkaline electrolyte injected into the battery, so that the alloy surface has an exposed surface (that is, a reaction surface). As a result, the charge / discharge reaction on the alloy surface rapidly progresses from the initial stage of the cycle, so that the initial characteristics are improved.

[0009]

【Example】

[Embodiment 1] FIG. 1 is a cross-sectional view of a cylindrical nickel-hydrogen alkaline storage battery using a hydrogen storage alloy electrode according to an embodiment of the present invention. A positive electrode 1 made of sintered nickel and a hydrogen storage alloy ( An electrode group 4 composed of a negative electrode 2 containing MmNi _3.1 Co _0.9 Al _0.2 Mn _0.5 ) and a separator 3 interposed between the positive and negative electrodes 1 and 2 is spirally wound. The electrode group 4 is arranged in an outer casing 6 which also serves as a negative electrode terminal, and a sealing body 8 is attached to an upper opening of the outer casing 6 via a packing 7 and inside the sealing body 8. A coil spring 9 is provided. The coil spring 9 is configured to be pressed in the direction of arrow A when the internal pressure inside the battery is abnormally increased, and the gas inside is released into the atmosphere. Further, the sealing body 8 and the positive electrode 1 are connected by a positive electrode conductive tab 10.

Here, the cylindrical nickel-hydrogen having the above structure
The alkaline storage battery was produced as follows. First,
Commercially available Mm (mixed with rare earth elements, which is a misch metal
Compound), Ni, Co, Al, and Mn in the element ratio of 1: 3.
Weigh each to a ratio of 1: 0.9: 0.2: 0.5
Then, melt it in an arc furnace in an argon-inert atmosphere.
I made a molten metal. Next, by cooling the molten metal
MmNi_3.1Co_0.9Al_0.2Mn_0.5Indicated by
A hydrogen storage alloy ingot was prepared. Then, this hydrogen storage
Mechanically rough so that the grain size of the gold ingot is 100 μm or less
The powder was pulverized to prepare a hydrogen storage alloy powder. Then this water
Elemental storage alloy powder and 5% by weight of aluminum oxide (Al ₂
O₃) And are filled in the ball mill, and then in the ball mill.
Fill with argon gas and rotate at room temperature for 2 revolutions at 80 rpm.
The mixture was stirred for 0 hour and mechanically alloyed. Only
After hydrogen storage, the mechanically alloyed hydrogen storage
Single layer of polyethylene oxide as a binder on gold powder
Add the amount% and mix them uniformly to keep pace.
Created. After this, paste this
Apply it to both sides of the punched metal core body
Negative electrode by drying at a temperature and further cutting to the specified size
2 was produced.

Next, an electrode group 4 composed of the negative electrode 2 and a known sintered nickel positive electrode 1 is formed through a separator 3 made of a non-woven fabric having alkali resistance, and then the electrode group 4 is connected to a battery can 6. Inserted inside. Then, this battery can 6
After pouring a 30% by weight KOH aqueous solution into the inside, the battery can 6 was further sealed to prepare a cylindrical nickel-hydrogen alkaline storage battery having a nominal capacity of 1000 mAh.

The battery thus produced is described below in (A
₁ ) Called battery. Examples 2 to 6 Al, ZrO instead of Al ₂ O _3
A battery was produced in the same manner as in Example 1 except that the negative electrode that was mechanically alloyed with ₂ , Zr, SiO ₂ , and Si was used.

The batteries thus produced are hereinafter referred to as (A ₂ ) battery to (A ₆ ) battery. [Examples 7 to 10] Addition amounts of Al ₂ O ₃ in the mechanical alloying treatment were 1 wt%, 10 wt%, 15 wt%,
A battery was prepared in the same manner as in Example 1 except that the negative electrode was changed to 20 wt%.

The batteries thus produced are hereinafter referred to as (A ₇ ) battery to (A ₁₀ ) battery, respectively. [Comparative Example] A battery was prepared in the same manner as in Example 1 except that a negative electrode not subjected to mechanical alloying treatment was used.

The battery thus manufactured is hereinafter referred to as (X) battery. [Experiment 1] (A ₁ ) battery to (A ₁₀ ) battery of the present invention,
The initial capacity was examined using the (X) battery of Comparative Example, and the results are shown in Table 1 below. In the experiment, the battery
The condition is that the battery is charged at 0.2C for 6 hours and then discharged at a current of 0.2C until the battery voltage reaches 1.0V. [Experiment 2] (A ₁ ) battery to (A ₁₀ ) battery of the present invention,
The cycle life (the time when the capacity was reduced to 50% of the initial capacity) was examined using the (X) battery of Comparative Example. The results are shown in Table 1 below together with the initial capacity. In the experiment, the battery was charged at a current of 1C for 1.2 hours, and then discharged at the same current of 1C until the battery voltage reached 1.0V. [Summary of Experiment 1 and Experiment 2]

[0016]

[Table 1]

As is apparent from Table 1 above, it is recognized that the batteries (A ₁ ) to (A ₁₀ ) of the present invention have a higher initial capacity than the battery (X) of the comparative example. This is because in the battery (X) of the comparative example, the hydrogen storage alloy that is the negative electrode is oxidized in the battery manufacturing process, whereas
₁₎ The cell ~ (A ₁₀₎ cell, the hydrogen storage alloy is coated with the alkali-soluble metal (or metal oxides), in the battery manufacturing process, it is not the hydrogen absorbing alloy is oxidized. On the other hand, it is considered that since the battery is dissolved in the KOH aqueous solution after the battery is manufactured, the charge / discharge reaction proceeds rapidly from the initial stage of the cycle.

It is also recognized that the batteries (A ₁ ) to (A ₁₀ ) of the present invention have a slightly improved cycle life as compared with the battery (X) of the comparative example. This is because the (X) battery of the comparative example inhibits the charge / discharge reaction due to the oxidation of the alloy surface, whereas the (A ₁ ) battery to (A ₁₀ ) battery of the present invention have the latter stage of the charge / discharge cycle. At the stage of
It is considered that the alkali-soluble metal (or metal oxide) that is not dissolved by the H aqueous solution remains, so that the oxidation of the alloy is inhibited. [Other Matters] In the above embodiment, Al (Al ₂ O ₃ ), Zr (Zr
O ₂ ), Si (SiO ₂ ), etc. were used, but the present invention is not limited to these. MmNi _3.1 Co as a rare earth hydrogen storage alloy
_{Although 0.9} Al _0.2 Mn _0.5 was used, the present invention is not limited to this. For example, Ti--Mn system, Ti
Even if a hydrogen storage alloy such as -Fe-based, Ti-Zr-based, Mg-Ni-based, Zr-Mn-based is used, the same effect as in the above-described embodiment can be obtained.

[0019]

As described above, according to the present invention, since the surface is coated with an alkali-soluble metal (or metal oxide), the hydrogen storage alloy is oxidized by oxygen in the air during the battery manufacturing process. There is no. On the other hand, after the battery is manufactured, the alkali-soluble metal (or metal oxide) is dissolved by the alkaline electrolyte injected into the battery, so that the alloy surface has an exposed surface (that is, a reaction surface). As a result, the charge / discharge reaction on the alloy surface rapidly progresses from the initial stage of the cycle, so that there is an excellent effect that the initial characteristics are improved.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional perspective view of a cylindrical nickel-hydrogen alkaline storage battery using a hydrogen storage alloy electrode according to an embodiment of the present invention.

[Explanation of symbols]

 2 Negative electrode

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Koji Nishio 2-18 Keihan Hondori, Moriguchi City Sanyo Electric Co., Ltd. (72) Inventor Nobuhiro Furukawa 2-18 Keiyo Hondori, Moriguchi City Sanyo Electric Co., Ltd. Within

Claims (1)

[Claims] 1. A hydrogen storage alloy electrode comprising a hydrogen storage alloy capable of reversibly storing and releasing hydrogen, wherein the alloy surface is coated with an alkali-soluble metal or its oxide. Hydrogen storage alloy electrode.