JPH0810592B2 - Sealed nickel and hydrogen storage battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application] The present invention relates to an improvement of a sealed nickel-hydrogen storage battery using a hydrogen storage alloy as a negative electrode material.

(Prior Art) An alkaline storage battery using a hydrogen storage alloy as a negative electrode material has attracted attention as a high energy density and low pollution battery, and a sealed nickel-hydrogen battery in combination with a nickel positive electrode has been proposed.

By the way, hydrogen storage alloy is an aqueous solution (electrolyte) when used.
It is easily oxidized in the inside, and a hydroxide is usually formed on the surface thereof, and the electrode capacity gradually decreases to reach the end of its life. Then, in a sealed nickel-hydrogen storage battery, oxygen is generated from the nickel positive electrode during overcharge, but when the hydrogen storage alloy deteriorates as described above, the reaction between oxygen and hydrogen stored in the alloy is hindered. Is not absorbed, and hydrogen is further generated from the hydrogen storage alloy negative electrode, which causes an increase in battery internal pressure.

Conventionally, a technique of adding cadmium or its oxide or hydroxide to a hydrogen storage alloy negative electrode has been proposed in order to prevent the above-described hydrogen storage alloy from being oxidized and prolonging its life. However, the presence of cadmium reduces the hydrogen storage capacity of the hydrogen storage alloy, that is, the electrode capacity, and therefore cannot be used as a battery.

(Problems to be Solved by the Invention) The present invention has been made to solve the above problems, and prevents oxidation of a hydrogen storage alloy in an electrolytic solution to prolong battery life and An object of the present invention is to provide a sealed nickel-hydrogen storage battery capable of preventing the internal pressure of the battery from rising due to generated oxygen and hydrogen.

[Structure of the Invention] (Means for Solving Problems) The sealed nickel-hydrogen storage battery of the present invention comprises a hydrogen storage alloy powder having an oxide film of an alloy component formed on at least a part of its surface, oxygen and hydrogen. A hydrogen storage alloy negative electrode containing a catalyst and a binder that promotes the reaction of, and a nickel oxide positive electrode and a nickel oxide positive electrode that are closely adhered via a separator are housed in an airtight container and filled with an electrolytic solution and sealed. It is a feature.

The hydrogen-absorbing alloy powder used in the present invention, on which an oxide film of an alloy component is formed on at least a part of the surface, is a simple method of activating and pulverizing the hydrogen-absorbing alloy and then exposing it to the air. Can be prepared by

Examples of the catalyst used in the present invention include carbon alone or carbon supported with at least one metal selected from platinum, palladium, rhodium, ruthenium, gold or silver.

(Function) According to such a sealed nickel-hydrogen storage battery, since the catalyst is added to the hydrogen storage alloy negative electrode, the reaction between oxygen and hydrogen generated in the battery is promoted and quickly returned to water. Therefore, it is possible to prevent the internal pressure of the battery from rising. Further, since the hydrogen storage alloy powder having the oxide film of the alloy component formed on the surface is used, it is possible to suppress the formation of hydroxide in the alkaline aqueous solution and prolong the battery life. Moreover, it is presumed that the oxide film enhances the action of the above-mentioned catalyst.

In the present invention, the thickness of the oxide film formed on the surface of the hydrogen storage alloy powder is preferably 2000 Å or less. This is because when the thickness of the oxide film exceeds 2000 liters, the reaction itself of hydrogen storage / release in the hydrogen storage alloy is hindered, the battery life cannot be extended, and the battery internal pressure rises. On the other hand, it is desirable that the film thickness of the oxide film is 50 Å or more. This has an oxide film thickness of 50Å
If it is less than the above range, the effect of suppressing the above-mentioned generation of hydroxide and enhancing the action of the catalyst becomes small, the battery life cannot be extended, and the battery internal pressure also rises.

(Example) Hereinafter, the Example of this invention is described with reference to drawings.

First, MmNi _4.2 Mn _0.8 (Mm is misch metal) was selected as a hydrogen storage alloy, an ingot of this alloy was housed in a pressure vessel, and hydrogen was stored and removed for activation and pulverization. After 96% by weight of this hydrogen storage alloy powder and 4% by weight of powdery polytetrafluoroethylene were mixed and kneaded, a sheet having a thickness of 0.5 mm was formed using a roller. This sheet-shaped molded product was stored in the air for 5 days, and then the surface thereof was measured by Auger electron spectroscopy. For example, the irradiation time of argon ion is 60
FIG. 3 shows the spectrum in the case of minutes. At the above irradiation time, a peak due to the constituent components appears at a depth of 1200 Å from the surface.

As is clear from FIG. 3, the components (N
In addition to the peaks of i, Mn) and the components (F, C) of the binder, an O peak was observed, and it was confirmed that an oxide film of the alloy component was formed.

Also, by changing the number of days stored in the air,
It was found that the thickness of the oxide film can be changed.

Example 1 First, LmNi _4.2 Mn _0.3 Al _0.3 Co _0.2 was selected as a hydrogen storage alloy, an ingot of this alloy was housed in a pressure resistant container, the inside of the container was depressurized to 10 ⁻⁵ Torr, and ice-cooled to about 5 ° C. rear,
The container was filled with 10 atm of hydrogen. When the alloy occludes hydrogen, the pressure in the container drops, so the container was refilled with hydrogen at 10 atm. This operation was repeated 4 times to cause the alloy to absorb hydrogen. Next, while heating the container to 80 ° C,
The hydrogen in the container was sucked and removed by a vacuum pump to completely release the hydrogen stored in the alloy. The occlusion powder finely pulverized through the above-mentioned process was mainly particles of 37 μm (400 mesh) or less. The alloy was transferred in an argon box without exposure to air. Then, a part of the alloy was taken out to the outside, and the number of days of storage in air was changed between 1 and 60 days to prepare several kinds of alloy samples having oxide films with different film thickness formed on the surface. The film thickness of the formed oxide film was measured by Auger electron spectroscopy.

Further, activated carbon supporting 5% by weight of platinum as a catalyst and powdery polytetrafluoroethylene (PTFE) as a binder were prepared.

The above hydrogen storage alloy, catalyst and binder were mixed and kneaded in a weight ratio of 94: 2: 4, respectively. Thereafter, each of these kneaded products was formed into a sheet having a thickness of 0.5 mm by using a roller, and further cut into a size of 85 mm × 41 mm. A nickel net with a lead portion (40 mesh, wire diameter 0.15 mm), which is a current collector, was pressed from one side of this sheet-shaped molded product by a press to produce a hydrogen storage alloy negative electrode.

On the other hand, as a nickel positive electrode, thickness 0.65 mm, size 65 mm ×
A sintered nickel electrode with 41 mm and theoretical capacity of about 800 mAh was prepared.

These hydrogen storage alloy negative electrode and nickel positive electrode are spirally wound through a separator made of polyamide nonwoven fabric to form an electrode body, which is made of an acrylic material whose inner shape is the same as that of a AA size battery case. The sealed nickel-hydrogen storage battery was assembled by enclosing it in an airtight container and filling 8N-KOH as an electrolytic solution and sealing it. A pressure sensor is attached to the closed container so that the internal pressure of the battery can be monitored.

For comparison, the alloy powder stored in the argon box was used, and a battery was assembled in the same manner as above in argon. In addition, for comparison, several kinds of alloy powders having oxide films with different film thickness formed on the surface and alloy powders having no oxide film formed on the surface were used without adding a catalyst, respectively A negative electrode was prepared and a battery was assembled in the same manner as above.

The battery assembled in this way had a capacity of about 700 mAh, so the nominal capacity was defined as 700 mAh.

Charge these batteries for 7.5 hours at 140mAh and discharge current to 3
A charging / discharging cycle test of discharging up to 1 V at 50 mAh was performed, and the discharge capacity in that cycle and the battery internal pressure at the end of charging in each cycle were measured.

The results of this charge / discharge cycle test are summarized in FIG. In Fig. 1, A is the number of cycles at which the discharge capacity became half of the nominal capacity, and B in the figure was the number of cycles at which the battery internal pressure reached 20 kg / cm ^2, and the film thickness of each oxide film. Is plotted against. In addition, A'in Fig. 1 is the number of cycles in which the discharge capacity is half of the nominal capacity in a battery in which no catalyst is added to the hydrogen storage alloy negative electrode, and B'in the figure is B'in the hydrogen storage alloy negative electrode. The battery internal pressure is
The number of cycles reaching 20 kg / cm ² is plotted against the film thickness of each oxide film.

As is clear from FIG. 1, the oxide film thickness is 50 to 20
It can be seen that the battery life is extended when 00Å. Also,
If the thickness of the oxide film exceeds 5000 Å, the battery life will be shorter than when the oxide film is not formed. On the other hand, when the catalyst is not added to the hydrogen storage alloy negative electrode, the battery life is not significantly changed regardless of whether the oxide film is formed or not.

Example 2 As a catalyst, activated carbon supporting 5% by weight of silver was used, and a hydrogen storage alloy powder, a catalyst and a binder were mixed at 94: 2: 4.
A battery was assembled in exactly the same manner as in Example 1 above, except that the hydrogen storage alloy negative electrode was prepared by mixing and kneading at the ratio. As for the comparative example, a battery corresponding to the case of the above-mentioned Example 1 was assembled.

Then, the same charge and discharge cycle test as in Example 1 was performed, and as shown in FIG. 2, almost the same results as in FIG. 1 were obtained.

In the present invention, the hydrogen storage alloy and the binder are not limited to those used in Examples 1 and 2, and various materials can be considered. As a hydrogen storage alloy, other than La-Ni system, La
-Co, Ca-Ni, Mg-Ni, Ti-Ni, Ti-Fe, Ti
Examples thereof include —Cr-based, Ti-V-based, or those in which some of the metal elements constituting these alloys are replaced with other metal elements. In addition to PTFE, polyethylene (PE), polystyrene (PS), carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA), or the like can be used as the binder. When an electrode is produced using these binders, various usages are conceivable, such as using in powder form or dissolving in a solvent (organic solvent, water, etc.) depending on the properties of each. .

The amount of catalyst is 10 when carbon such as activated carbon is used alone.
Weight% or less, activated carbon, etc. with platinum, palladium, rhodium,
In the case of a supported catalyst supporting ruthenium, silver, gold, etc., if the supported amount of these noble metals is 0.1% by weight or more based on the amount of carbon, it is desirable that the total amount is 5% by weight or less. This is because when the catalyst amount exceeds the above range, the electrode capacity is reduced.

[Effects of the Invention] As described in detail above, according to the present invention, the battery life is long,
It is possible to provide a sealed nickel-hydrogen storage battery capable of preventing an increase in battery internal pressure due to oxygen and hydrogen generated in the battery.

[Brief description of drawings]

FIG. 1 shows that the thickness of the oxide film and the discharge capacity of the sealed nickel-hydrogen storage battery in Example 1 of the present invention are 1/2 of the nominal capacity.
Until the number of charge / discharge cycles and battery internal pressure is 20kg / cm ²
FIG. 2 is a characteristic diagram showing the relationship with the number of charge / discharge cycles until reaching the temperature, FIG. 2 shows the film thickness of the oxide film and the nominal capacity of the discharge capacity of the sealed nickel-hydrogen storage battery in Example 2 of the present invention.
Number of charge / discharge cycles and battery internal pressure up to 1/2 is 20 kg /
FIG. 3 is a characteristic diagram showing the relationship with the number of charge / discharge cycles until reaching cm ² , and FIG. 3 is a spectrum diagram by Auger electron spectroscopy analysis of the surface of the hydrogen storage alloy negative electrode.

Front page continuation (72) Inventor Yuji Sato 1 Komukai Toshiba-cho, Kouki-ku, Kawasaki-shi, Kanagawa Inside Toshiba Research Institute Co., Ltd. (56) Reference JP-A-62-15760 (JP, A)

Claims (3)

[Claims] 1. A hydrogen storage alloy having an oxide film of an alloy component formed on at least a part of its surface, a hydrogen storage alloy negative electrode containing a catalyst and a binder for promoting a reaction between oxygen and hydrogen,
A sealed nickel-hydrogen storage battery, characterized in that an electrode body, which is in close contact with a nickel oxide positive electrode via a separator, is housed in a sealed container and filled with an electrolytic solution and sealed. 2. The sealed nickel-hydrogen storage battery according to claim 1, wherein the oxide film has a thickness of 2000 liters or less. 3. A catalyst comprising carbon alone or at least one carbon selected from platinum, palladium, rhodium, gold or silver.
The sealed nickel-metal hydride storage battery according to claim 1, wherein the sealed nickel-hydrogen storage battery is made of a material carrying a kind of metal.