JPH0650634B2 - Hydrogen storage electrode - Google Patents

Description

The present invention relates to an electrochemical storage and desorption of hydrogen as an anode of an alkaline storage battery, in particular, an alkaline storage battery using a nickel electrode, an air electrode, a silver oxide electrode or the like as a positive electrode. A hydrogen storage electrode capable of

2. Description of the Related Art Lead storage batteries, nickel-cadmium storage batteries, and the like are well known as general-purpose storage batteries, but these storage batteries have relatively low energy density per weight or volume. Therefore, recently, a nickel-hydrogen storage battery having a large energy density, in which a certain alloy capable of electrochemically absorbing and desorbing a large amount of hydrogen electrochemically is used as a negative electrode and nickel oxide is used as a positive electrode, has been proposed. . As a negative electrode of such a storage battery, a relatively good one is Ti-Ni system, La (or M
m) -Ni series, Ca-Ni series, and substitution products based on these. In addition, recently, Ti _2-x Zr _x V
_A patent (USP 4,551,400) in which _4-y Ni _y , 0 <x ≦ 1.5, 0.6 ≦ y ≦ 3.5 is applied.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention However, although the Ti—Ni alloy has a relatively high discharge capacity due to electrochemical charging and discharging, it forms a stable phase of Ti during repeated charge and discharge cycles. Therefore, there is a main problem in the life performance as a battery, and the La (or Mm) -Ni-based alloy has a relatively small discharge capacity because the electrochemical hydrogen storage capacity is not sufficient, and it is resistant to temperature changes. There are problems such as large fluctuations in performance and high alloy prices. And Ca-N
Although the i-based alloy has a high discharge capacity at the beginning of the charging / discharging cycle, it has a drawback that, like the Ti—Ni-based alloy, its performance is significantly deteriorated by repeating charging / discharging. _{Further, Ti 2-x Zr x V} 4-y Ni y, 0
When <x ≦ 1.5 and 0.6 ≦ y ≦ 3.5, gradually stable hydrides are formed, and there is a problem in cycle life characteristics.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a hydrogen storage electrode capable of obtaining a storage battery having a particularly high discharge capacity and a long life.

Means for Solving the Problems The hydrogen storage electrode of the present invention has at least the nominal composition formula Zr.
Mo _α Ni _β (where α = 0.1 to 1.2 and β = 1.
1 to 2.5) is provided with a metal material containing an alloy phase as a hydrogen storage / desorption material.

Action Compositional formula ZrMo _α Ni _β (where α = 0.1 to 1.
2, β = 1.1 to 2.5) is an alloy represented by hydrogen atoms occupying the unit cell under the normal electrochemical conditions that occur in alkaline storage batteries, as compared with the conventional hydrogen storage alloy. Due to the large number, the storage and desorption of hydrogen is large,
The hydrogen absorption / desorption reaction rate is also high. Further, even if the hydrogen storage / desorption cycle is repeated, stable hydride phases and oxide phases are not generated, so the hydrogen storage electrode equipped with these as the main material follows rapid charging / discharging and has a high electric capacity for a long time. Can be maintained over.

Example The inventors of the present invention have developed a Ti-Ni-based hydrogen storage alloy, AB ₅ type (A: rare earth such as Mm, La, B: Ni, Co, Cr
Etc.) Various types of higher performance CD ₂ type (C: Ti group elements, D: Fe, V, Cr, Co, Ni, etc.) alloys that replace hydrogen storage alloys, and hydrogen storage electrodes (negative electrodes) for alkaline storage batteries. As a result of examining the performance as
It has been found that the r-Mo-Ni alloy phase has particularly excellent properties.

For example, a Larvus phase C15 type alloy belonging to the CD ₂ type alloy has a cubic MgCu ₂ type crystal structure, and the inventors of the present invention have previously reported the performance as a hydrogen storage material.
As shown in Japanese Patent Publication No. 1, the main factors are heat of hydride formation, crystal lattice constant a, and crystal homogeneity. However, when an alloy satisfying these factors and having an excellent hydrogen storage property in the hydrogen gas phase is used as it is as a hydrogen storage electrode in an alkaline electrolyte, in addition to the hydrogen storage capacity, the electrochemical stability in the electrolyte is high. Not only is the catalyst performance a problem, but the charge electricity quantity is sufficiently large but the discharge electricity quantity may be small, so it cannot be said that it is necessarily suitable as a hydrogen storage electrode.

However, the present inventors have found that CD ₂ type alloys such as C1
It was found that only a special range of alloy phases of 5 type or C14 type was excellent as a hydrogen storage electrode,
I proposed earlier. The present application is a further improvement of the inventors' prior inventions, and in particular, was completed by making initial activation characteristics, charge / discharge cycle life characteristics and charge / discharge electric capacity more practically valuable.

Specific examples will be described below.

Commercially available Zr, Mo, and Ni were used as raw materials and melted in an argon arc melting furnace or an argon high-frequency furnace to obtain, for example, an alloy having the composition shown in the following table. A part of the melted alloy sample is used for alloy analysis such as alloy composition, crystal structure, crystal lattice constant, and homogeneity, and the rest is for measuring hydrogen storage amount in hydrogen gas (mainly P (pressure) -C). (Composition) -T (temperature) measurement) and electrode performance evaluation. Alloy No. in the table 1 to 6 are examples of alloys according to the present invention, and N
o. 7 to 10 are composed of the same constituent elements as in the present invention, but the atomic ratio is outside the range of the present invention.

That is, No. Regarding the atomic ratio α of Mo, 7 and 8 are alloys with too large α (No. 7) and alloys with too small α (No. 8)
And No. Regarding the atomic ratio β of Ni, Nos. 9 and 10 are alloys with too small β (No. 9) and alloys with too large β (No.
A representative example of 10) is shown.

The alloys shown in the above table were evaluated for performance as a negative electrode for alkaline storage batteries. First, the alloy obtained by melting is pulverized into particles of 400 mesh or less, and about 5 g of this alloy powder is added to 0.5 g of polyethylene powder as a binder.
And 2 g of carbonyl nickel powder as a conductive agent are mixed and stirred sufficiently, and this is pressed into a plate shape by pressing around a nickel screen (wire diameter 0.2 mm, 16 mesh) as a conductive core material. did. This is 120
After being placed in a vacuum at 1 ° C. for 1 hour and heating to melt polyethylene, a lead was attached to form a hydrogen storage electrode.

For evaluation as a negative electrode for a storage battery, a commercially available sintered nickel electrode was selected as a positive electrode, a polyamide nonwoven fabric was used as a separator, and a solution of 20 g / 1 of lithium hydroxide added to a caustic potash aqueous solution having a specific gravity of 1.30 was used as an electrolytic solution. The charging and discharging were repeated at a constant current. The amount of electricity charged at this time is 500mA
× 4 hours, discharge was performed at 250 mA, and 0.8 V or less was cut. As an example of the results, the discharge electric capacity at the 10th charge / discharge cycle is shown in the above table, and the charge / discharge cycle characteristics are shown in the figure. In the figure, the horizontal axis represents the number of charge / discharge cycles (∞), and the vertical axis represents the discharge electric capacity per gram (T).
i ₂ Ni, LaNi ₅ ) and alloy examples outside the range (No.
7 to 10). The numbers in the figure are alloy Nos. In the above table. Is consistent with

As is apparent from the table and the figures, the alkaline storage battery negative electrode having the hydrogen storage alloy according to the present invention as a main constituent element has a large discharge capacity, and has excellent cycle life characteristics (durability) and initial discharge rising characteristics. I understand. In addition, rapid charge / discharge characteristics at large current were also good. On the other hand, alloys with an atomic ratio α of less than 0.1 or greater than 1.2 have a small discharge capacity, or alloys with an atomic ratio β of less than 1.1 or greater than 2.5 have a discharge capacity of Is small. The reason for this is that the V content α is particularly related to the amount of electricity charged, and the larger the amount of Mo, the greater the amount of electricity charged, but because a stable hydride is formed, the discharge efficiency is small and the amount of electricity discharged is small. Further, the Ni content is particularly related to the charge / discharge cycle characteristics (durability), and the more Ni, the longer the life, but the less the charge electricity tends to be. When the discharge capacity is evaluated from a practical point of view, 250 mAh / g is necessary. From the above points and the homogeneity and stability of the alloy phase,
It is represented by the general formula ZrMo _α Ni _β , and α = 0.1 to 1.2
Only the alloy phase in the range of 0, β = 1.1 to 2.5 is excellent from a practical viewpoint. Further, as is apparent from the table, a particularly preferable composition range is α = 0.3 to 0.7, β =
It is 1.4 to 1.9. The electrode of the present invention in this range exhibits a discharge electricity quantity (10th cycle) of 350 mAh / g or more, and has a particularly high capacity, a long life and economically excellent.

Further, as can be seen from the cycle life characteristics of the figure, the conventional Ti ₂ Ni, LaNi ₅ is significantly deteriorated, whereas the hydrogen storage electrode of the present invention has good cycle life characteristics regardless of the discharge capacity. Therefore, it can be seen that it is practical. This is due to the excellent electrochemical catalyst performance and oxidation resistance performance.

The present invention has alloys of various compositions other than those shown in the table. In this case, naturally, the main alloy phase is represented by the general composition formula ZrMo _α Ni _β , and the atomic ratios α and β are respectively
Includes phases in the range of α = 0.1 to 1.20 and β = 1.1 to 2.5. From the above, it can be seen that the hydrogen storage electrode for an alkaline storage battery using the alloy of the present invention has a higher capacity, excellent initial discharge capacity characteristics, and a longer life than those of the conventional ones. Further, the electrode of the present invention can be applied to a hydrogen electrode of a fuel cell, an electrode for electrolysis, a capacitor, etc., in addition to the electrode of the alkaline storage battery.

EFFECTS OF THE INVENTION The hydrogen storage electrode of the present invention can have a high capacity, has good initial charge / discharge characteristics, is excellent in reversibility of the reaction, and has a great effect in prolonging its life. In addition, since the raw materials are relatively low in price, the electrode manufacturing technology can be sufficiently handled by the conventional technology.

[Brief description of drawings]

The figure is a cycle life characteristic diagram of the hydrogen storage electrode and the reference electrode of one example of the present invention.

Claims (4)

[Claims] 1. At least a nominal composition formula ZrMo _α Ni _β
(However, α = 0.1 to 1.2, β = 1.1 to 2.5)
Hydrogen absorption of metallic materials containing alloy phases represented by
A hydrogen storage electrode provided as a discharge material. 2. The hydrogen storage electrode according to claim 1, wherein α = 0.3 to 0.7. 3. The hydrogen storage electrode according to claim 1, wherein β = 1.4 to 1.9. 4. An alloy phase having at least one kind of C15 (M
The hydrogen storage electrode according to claim 1, comprising a crystalline material having a gCu ₂ ) type crystal structure.