JPH0650633B2 - 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 from ECD of the United States,
_{Ti 2-x Zr x V 4} -y Ni y, 0 <x ≦ 1.5,
Patents with 0.6 ≦ y ≦ 3.5 (USP 4,551,40
No. 0) has been filed.

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, stable hydrides are formed, so that there remains 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 substantially the same general formula ZrV _α Ni.
_β (However, α = 0.01 to 1.20, β = 1.0 to
The alloy phase represented by 2.5) is provided as a main hydrogen absorbing / desorbing material.

Action General formula ZrV _α Ni _β (where α = 0.01 to 1.2
The alloy represented by 0, β = 1.0 to 2.5) has a larger number of hydrogen atoms occupying the unit cell under electrochemical conditions than the conventional hydrogen storage alloy described above, and therefore has a larger number of hydrogen atoms. It has a large absorption and desorption amount and a high hydrogen absorption / desorption reaction rate. 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 used C15 type (MgCu ₂ type) or C1 type.
As a result of investigating the performance of various types of 4 type (MgZn ₂ type) Larvus phase alloys as a hydrogen storage electrode (negative electrode) for alkaline storage batteries, it was found that the Zr-V-Ni type alloy phase has excellent characteristics. It was

For example, the C15 type alloy belonging to the Larvus phase is cubic Mg
It has a Cu ₂ -type crystal structure, and the performance as a hydrogen storage material is, as the present inventors have previously shown in Japanese Patent Publication No. 56-31341, the crystal lattice constant a and the crystal homogeneity as main factors. To do. However, when an alloy having excellent hydrogen storage characteristics in the hydrogen gas phase is used as it is as a hydrogen storage electrode in an alkaline electrolyte, not only the hydrogen storage amount but also electrochemical stability in the electrolyte becomes a problem. In some cases, the amount of electricity charged was sufficiently large but the amount of electricity discharged was small. Therefore, it cannot be said that the hydrogen storage electrode is necessarily suitable.

However, the present inventors have found that only the alloy phase having a special composition range among the C15 type and the C14 type is excellent as a hydrogen storage electrode, and previously proposed. This application is a further improvement of the inventors' prior invention, and in particular,
The charging / discharging cycle life characteristics and the charging / discharging electric capacity have been completed to have practical value.

Specific examples will be described below.

Commercially available Zr, V, 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)
It was used for measurement) and electrode performance evaluation.

Alloy No. in the table 1 to 7 are examples of the alloy according to the present invention, and 8 to 11 are composed of the same constituent elements as those of the present invention, but the atomic ratio is outside the scope of the present invention. That is, No. 8,
No. 9 is an alloy in which the atomic ratio α of V is too large (No. 8), an alloy in which it is too small (No. 9), and No. 9 10 and 11 are Ni
Representative examples of the alloy (No. 10) whose atomic ratio β is too small and the alloy (No. 11) which is too large are 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 200 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. 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 excellent cycle life characteristics (durability). In addition, rapid charge / discharge characteristics at large current were also good. On the other hand, an alloy having an atomic ratio α of less than 0.01 or more than 1.20 has a small discharge capacity, and an atomic ratio β of less than 1.0, or
Alloys larger than 2.5 also have small discharge capacity. The reason for this is that the content α of V is particularly related to the amount of electricity charged, and the higher the amount of V, the greater the amount of electricity charged, but because a stable hydride is formed, the discharge efficiency decreases. In addition, the Ni content is particularly related to the charge / discharge cycle characteristics. The more Ni, the longer the life, but the smaller the amount of electricity charged. When the discharge capacity is evaluated from a practical point of view, 250 mAh / g is necessary as shown in the above table and figures. From the above points and the homogeneity and stability of the alloy phase, the alloy phase represented by the general formula ZrV _α Ni _β and in the range of α = 0.01 to 1.20 and β = 1.0 to 2.5. Only good from a practical point of view.
Further, as can be seen from the table, a particularly preferable composition range is α
= 0.1 to 0.6 and β = 1.4 to 1.9. The electrode of the present invention in this range shows a discharge electricity quantity (10th cycle) of 350 mAh / g or more, has a long life, and is particularly economically excellent.

Further, as can be seen from the cycle life characteristics in the figure, the conventional Ti ₂ Ni, LaNi ₅ is significantly deteriorated, whereas the hydrogen storage electrode of the present invention has a long life even if the initial discharge capacity is somewhat small. Since the characteristics are good, it can be seen that it is practical. This is due to the excellent electrochemical catalytic performance and oxidation resistance.

The present invention can be applied to many alloy compositions other than those shown in the table. In this case, naturally, the main alloy phase is represented by the general formula Z
rV _α Ni _β , and atomic ratios α and β are α =
It is in the range of 0.01 to 1.20 and β = 1.0 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 and a longer life than 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, is excellent in the reversibility of the reaction, and has a great effect in extending the life. Further, since the raw materials are relatively low in price and the electrode manufacturing technology can be sufficiently dealt with by the conventional technology, the industrial value is great.

[Brief description of drawings]

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

Claims (4)

[Claims] 1. A substantially general formula ZrV _α Ni _β (where
A hydrogen storage electrode composed of an alloy phase represented by α = 0.01 to 1.20 and β = 1.0 to 2.5). 2. The hydrogen storage electrode according to claim 1, wherein α = 0.1 to 0.6. 3. The hydrogen storage electrode according to claim 1, wherein β = 1.4 to 1.9. 4. The hydrogen storage electrode according to claim 1, wherein the alloy phase is made of at least one crystalline material.