JPH08134567A - Hydrogen storage alloy and hydrogen storage alloy electrode for alkali battery - Google Patents

Abstract

PURPOSE: To inhibit the formation of an oxidized film on the surface of an AB2 type Laves phase alloy forming an electrode without reducing the volume of the electrode or the energy density per unit weight by adding a specified amt. of B and/or Si to the alloy. CONSTITUTION: This alloy has a compsn. represented by the formula Zn1-x Tix Niα Vbα Mncα Fe(1-a-c)α Rβ(where R is at least one of B and Si, 0<=x<=0.9, 1.5<=α<=2.0, 0<β<=0.2, 0.4<=a<=0.7, 0.1<=b<=0.3 and 0.1<=c<=0.32). The structure of Laves phase is converted into a nearly amorphous structure by adding B or Si, the formation of an oxidized film on the surface of this alloy is inhibited and discharge capacity at the time of high-rate discharge can be increased without requiring coating with Ni, Cu, etc., for preventing poisoning.

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 and a hydrogen storage alloy electrode used as a negative electrode material for alkaline storage batteries.

[0002]

2. Description of the Related Art As a storage battery having a high energy density, an alkaline storage battery using a hydrogen storage alloy as a negative electrode material is known. As the hydrogen storage alloy, LaNi ₅ , MmNi ₅
AB _{5 type} such as (Mm: misch metal) or ZrM
The AB ₂ form having a Laves phase structure such as n ₂ is known. The AB _{5 type} is easy to activate early, and the AB _{2 type} can achieve high capacity. Among AB ₂ type hydrogen storage alloys, the composition formula Zr _{1- X} Ti _X M _α (1.5 ≦ α ≦
2.5), and in this kind of hydrogen storage alloy, Ni, Co, Mn, Al, Cr, Fe, Cu, S
By using at least one selected from n, Sb, Mo, V, and Zn as M (B site in AB ₂ type), it is possible to increase the capacity of the battery.

A battery using a hydrogen storage alloy having a Laves phase structure has a problem that it is poisoned by oxygen in the atmosphere and the discharge capacity at the time of high rate discharge is reduced. Therefore, JP-A-61-64069 and JP-A-61-1
As disclosed in Japanese Patent No. 01957, it has been proposed to coat the surface of a crushed hydrogen storage alloy with corrosion resistant nickel, copper or the like to prevent poisoning. In addition, as shown in JP-A-4-232202 and JP-A-4-245165,
It has been proposed to prevent the poisoning of the hydrogen storage alloy by making a hydrogen storage alloy electrode by mixing pyrolytic carbon, iron or an iron alloy with hydrogen storage alloy powder.

[0004]

However, when the surface of the hydrogen storage alloy is coated with nickel, copper or the like, there is a problem that the production of the hydrogen storage alloy becomes complicated.

When such a coating is applied or when pyrolytic carbon, iron or an iron alloy is mixed with hydrogen storage alloy powder, a coating (nickel, copper) or a mixture (pyrolytic carbon, iron or iron alloy) is obtained. ), There is a problem that the energy density per volume and weight of the hydrogen storage alloy electrode is reduced.

Further, when manufacturing a hydrogen storage alloy electrode,
A general method is to fill a foam metal substrate with a paste prepared by kneading a hydrogen storage alloy powder with a water-soluble binder. When a hydrogen storage alloy electrode is manufactured in this manner, the alloy powder is dipped in a water-soluble binder and dried, so that an oxide film is formed on the surface of the alloy powder and the discharge capacity at the time of high rate discharge of the battery decreases. There was a problem.

An object of the present invention is to provide a hydrogen storage alloy capable of suppressing the formation of an oxide film on the surface without lowering the energy density per volume and weight of the electrode. Another object of the present invention is to provide a hydrogen storage alloy electrode for an alkaline storage battery, which is capable of suppressing the formation of an oxide film on the surface of the hydrogen storage alloy and increasing the discharge capacity during high rate discharge of the battery.

[0008]

DISCLOSURE OF THE INVENTION The present invention aims to improve a hydrogen storage alloy, and has a composition formula of Zr _1-X Ti _X Ni _aα V
_bα Mn _cα Fe _{(1-abc) α} R _β
Is at least one of B and Si, and the range of X is 0
≦ X ≦ 0.9, the range of α is 1.5 ≦ α ≦ 2.5, the range of β is 0 <β ≦ 0.3, and the ranges of a, b, and c are 0.4 ≦ a, respectively. ≦ 0.7, 0.1 ≦ b ≦ 0.3,
0.1 ≦ c ≦ 0.32.

By using such a hydrogen storage alloy, it is possible to obtain a hydrogen storage alloy electrode for an alkaline storage battery which can increase the discharge capacity during high rate discharge of the battery.

[0010]

The hydrogen storage alloy of the present invention suppresses the formation of an oxide film on the surface without using a coating or mixture,
Poisoning due to atmospheric oxygen can be prevented. Therefore, it is possible to suppress the decrease in discharge capacity during high rate discharge of the battery without decreasing the energy density per volume and weight of the electrode. Further, according to the present invention, Zr, Ni, B, S
By optimizing the amount of i, the corrosion resistance of the hydrogen storage alloy can be increased and the cycle life of the battery can be extended. It is considered that this is due to the following reasons. Generally, many elements of A site and B site that form an alloy having a Laves phase structure of AB _{2 type} are 1.25 to 1.6.
It has an atomic radius of 2 Å. And
The interatomic distance of the hydrogen storage alloy is determined by the atomic radii of these elements. Boron or silicon has an atomic radius of 1.2
Since the specific gravity is less than 5 angstrom and the melting point is low, when the amount of boron (B) or silicon (Si) in the range of the present invention is contained in the hydrogen storage alloy, Zr
The lattice radius of the Laves phase structure of the hydrogen storage alloy is disordered at the atomic level. As a result, it has a structure close to amorphous when viewed microscopically. Therefore, it is possible to suppress the formation of an oxide film on the surface of the Zr-based hydrogen storage alloy.
By setting the ranges of X, α, β, a, b, and c to the ranges of the present invention, it is possible to suppress a decrease in discharge capacity during high rate discharge of the battery and extend the cycle life. When X exceeds 0.9, the crystal lattice volume becomes small, the hydrogen storage amount decreases, and the capacity decreases. When α is less than 1.5 or more than 2.5, phases other than AB _{2 type} are formed, the hydrogen storage amount is reduced, and the capacity is reduced. When β exceeds 0.3, B and Si are precipitated and the capacity is reduced. When a is less than 0.4, the corrosion resistance is reduced and the cycle life is shortened. When a exceeds 0.7, the contents of Mn and V in the alloy decrease, so that the hydrogen storage amount decreases and the capacity decreases. When b is less than 0.1, a phase other than AB _{2 type} is formed, and the hydrogen storage amount is reduced and the capacity is reduced. b is 0.3
If it exceeds, the corrosion resistance is lowered and the cycle life is shortened. If c is less than 0.1, a phase other than AB _{2 type} is formed, and the hydrogen storage amount is reduced and the capacity is reduced. c is 0.3
If it exceeds 2, corrosion resistance is lowered and cycle life is shortened.

Although it is an AB _{5 type} hydrogen storage alloy,
As disclosed in JP-A-3-280357, a hydrogen storage alloy electrode in which boron is contained in a hydrogen storage alloy has been proposed. In this type of hydrogen storage alloy electrode, the contained boron is present in a deposited form, cracks occur in the hydrogen storage alloy at the beginning of battery charging, and the specific surface area of the alloy increases. Therefore, the electrolytic solution can easily penetrate into the alloy, and the initial discharge capacity can be increased. This technique is applied to AB ₂ form hydrogen-absorbing alloy, the inclusion of boron AB ₂ form hydrogen-absorbing alloy, unlike the AB ₅ form, crack was observed in the alloy even after repeated charge-discharge cycles 10 cycles Although not present, a hydrogen storage alloy having an active capacity and a high capacity at the time of high rate discharge can be obtained from the beginning of the charge / discharge cycle.

[0012]

EXAMPLES Commercially available zirconium (Zr), titanium (T
i), nickel (Ni), vanadium (V), manganese (Mn), iron (Fe), boron (B), silicon (Si)
Was weighed in a predetermined amount and put in a copper crucible arranged in a vacuum arc melting furnace. Then, the metal was heated and melted in a vacuum arc melting furnace in a 99.99% argon atmosphere, and Examples 1 to 19 and Comparative Examples 1 to 1 shown in Table 1 below.
About 40 g of button-shaped alloy ingots each having 15 Laves phase structure were prepared. Then, these alloy lumps were pulverized to prepare a hydrogen storage alloy powder that passed through a 200 mesh mesh. Next, each hydrogen storage alloy was kneaded with an aqueous solution of 1.0% by weight of polyvinyl alcohol to prepare pastes. Then, each paste was filled in a foamed nickel substrate, dried, and pressed to a thickness of 0.4 mm to form a hydrogen storage alloy electrode (negative electrode). The weight of the hydrogen storage alloy powder in the hydrogen storage alloy electrode was 1.0 g each. Next, each hydrogen storage alloy electrode (negative electrode) and a known nickel electrode (positive electrode) using nickel hydroxide as an active material are laminated via a nylon separator, and the separator is filled with 30
Each of the open type alkaline storage batteries for test was made by impregnating with an electrolytic solution composed of an aqueous solution of potassium hydroxide of wt%.

[0013] These test alkaline storage batteries 100mA
The discharge capacity was determined by discharging at currents of / g, 200 mA / g, and 500 mA / g. In addition, each battery was charged at 120 mA for 5 hours and then repeatedly charged and discharged at a final voltage of 1.0 V at 100 mA / g to measure the number of cycles at which each battery reached the end of its life. Table 2 shows the measurement results. Table 2
Is the composition formula of the hydrogen storage alloy of each battery Zr _1-X Ti _X Ni
X in _aα V _bα Mn _cα Fe _{(1-abc) α} R _β ,
Numerical values of α, β, a, b, and c are also shown.

[0014]

[Table 1]

[Table 2] From Table 2, the composition formula Zr _1-X Ti _X Ni _aα V _bα Mn _cα
When the hydrogen storage alloy of Comparative Example 2 in which X of Fe _{(1-abc) α} R _β exceeds 0.9 is used, the discharge capacity (200 mAh / g) required at a discharge current of 200 mA / g is significantly lower. It Therefore, the Ti substitution amount X of Zr needs to be 0.9 or less. Further, it can be seen that the cycle life is shortened when the hydrogen storage alloy of Comparative Example 3 in which a is less than 0.4 is used. It can be seen that when the hydrogen storage alloy of Comparative Example 4 in which a exceeds 0.7 is used, the discharge capacity decreases. Therefore,
The substitution amount a of Ni must be 0.4 ≦ a ≦ 0.7. Further, it can be seen that the cycle life is shortened when the hydrogen storage alloy of Comparative Example 5 in which b exceeds 0.3 is used. It can be seen that the discharge capacity decreases when the hydrogen storage alloy of Comparative Example 6 in which b is less than 0.1 is used. Therefore, the substitution amount b of V needs to be 0.1 ≦ b ≦ 0.3. Also, c is 0.3
It can be seen that the cycle life is shortened when the hydrogen storage alloy of Comparative Example 7 exceeding 2 is used. It can be seen that the discharge capacity decreases when the hydrogen storage alloy of Comparative Example 8 in which c is less than 0.1 is used. Therefore, the substitution amount c of Mn is 0.1 ≦ c ≦
It should be 0.32. Further, it can be seen that the discharge capacity decreases when the hydrogen storage alloy of Comparative Example 9 in which α is less than 1.5 is used. It can be seen that when the hydrogen storage alloy of Comparative Example 10 in which α exceeds 2.5 is used, the discharge capacity decreases, and as a result, the discharge capacity per weight decreases. Therefore, α
The value of must be 1.5 ≦ α ≦ 2.5.

Next, a battery using the hydrogen storage alloy of Example 3 (hydrogen storage alloy containing boron) and a battery using the hydrogen storage alloy of Comparative Example 11 (hydrogen storage alloy not containing boron) were respectively subjected to electric current. The discharge was performed while changing the amount (discharge rate), and the change in the discharge capacity of each battery was examined. The hydrogen storage alloy of Example 3 and the hydrogen storage alloy of Comparative Example 11 have almost the same composition except for boron. FIG. 1 shows the measurement result. From this figure, when the hydrogen storage alloy containing boron (Example 3) was used, the discharge capacity of the battery did not decrease significantly even when the discharge current was increased, whereas the hydrogen storage alloy containing no boron (Comparative Example). It can be seen that when 11) is used, the discharge capacity of the battery decreases remarkably as the discharge current increases.

Next, the substitution amount β of boron (B) is 0 to 0.5.
The composition is the same (Z
r _0.5 Ti _0.5 Ni _1.1-β V _0.5 Mn _0.2 Fe _0.2 B
Batteries using the hydrogen storage alloys of Examples 4 to 8, Comparative Examples 1 and 12 having _β ) were discharged at a current of 500 mA / g. Then, the discharge capacity of each battery was measured to examine the change in the discharge capacity of the battery depending on the substitution amount β of boron (B). FIG. 2 shows the measurement result. From this figure, in the hydrogen storage alloy containing no boron (β = 0), the discharge capacity was 70 mAh / g, while the content of boron was 0.001.
The discharge capacity increases dramatically (135m
Ah / g). When the content of boron increases to 0.05 mol, the discharge capacity increases, and when it exceeds 0.05 mol, the discharge capacity decreases, and when the content of boron exceeds 0.3 mol, hydrogen containing no boron is contained. It can be seen that the discharge capacity is reduced to almost the same as that of the battery using the storage alloy.

Next, the substitution amount β of silicon (Si) is 0 to 0.
The composition is different in the range of 3 mol, and the other is almost the same composition (Zr _0.5 Ti _0.5 Ni _1.1-β V _0.5 Mn _0.2 Fe
Examples 12 to 16 with a _0.2 Si _beta), a battery using the hydrogen storage alloy of Comparative Example 12 was discharged at 500mA / g of current. Then, the discharge capacity of each battery was measured to examine the change in the discharge capacity of the battery depending on the substitution amount β of silicon (Si). FIG. 3 shows the measurement result. From the figure, it can be seen that the hydrogen storage alloy containing no silicon (β = 0) has a discharge capacity of 70 mAh / g, while the discharge capacity of silicon is 0.00
The discharge capacity dramatically increases by only including 1 mole (120
mAh / g). Then, the discharge capacity increases up to a content of 0.01 mol of boron, the discharge capacity decreases when the content of boron exceeds 0.01 mol, and the hydrogen does not contain boron when the content of boron exceeds 0.3 mol. It can be seen that the discharge capacity is reduced to almost the same as that of the battery using the storage alloy. Therefore, according to FIGS. 1 to 3, the range of β needs to be 0 <β ≦ 0.3.

[0018]

According to the hydrogen storage alloy of the present invention, the formation of an oxide film on the surface can be suppressed and poisoning by oxygen in the atmosphere can be prevented without using a coating or mixture. Therefore, it is possible to suppress the decrease in discharge capacity during high rate discharge of the battery without decreasing the energy density per volume and weight of the electrode. According to the present invention, Zr, Ni,
By optimizing the amounts of B and Si, the corrosion resistance of the hydrogen storage alloy can be enhanced and the cycle life of the battery can be extended.

[Brief description of drawings]

FIG. 1 is a battery using a hydrogen storage alloy containing boron,
It is a figure which shows the difference of the change of discharge capacity with the amount of current (discharge rate) with the battery using the hydrogen storage alloy which does not contain boron.

FIG. 2 is a diagram showing a change in discharge capacity of a battery depending on a substitution amount β of boron (B).

FIG. 3 is a diagram showing a change in discharge capacity of a battery depending on a substitution amount β of silicon (Si).

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[Procedure amendment]

[Submission date] June 29, 1995

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be amended] Title of invention

[Correction method] Change

[Correction content]

Title: Hydrogen storage alloy and hydrogen storage alloy electrode for alkaline storage battery

[Procedure Amendment 2]

[Document name to be amended] Statement

[Name of item to be amended] Claims

[Correction method] Change

[Correction content]

[Claims]

Front page continuation (72) Inventor Yuji Ishii 2-1-1, Nishishinjuku, Shinjuku-ku, Tokyo Within Shinjin Todenki Co., Ltd. Hitachi Ltd., Hitachi Research Laboratory (72) Inventor, Keiko Igawa, 7-1, 1-1, Omika-cho, Hitachi City, Ibaraki Prefecture Hitachi Ltd., Hitachi Research Laboratory, (72) Inventor, Shoko Tanikoshi, 7-chome, Omika-cho, Hitachi City, Ibaraki No. 1 in Hitachi, Ltd. Hitachi Research Laboratory

Claims (2)

[Claims] 1. A composition formula Zr _1-X Ti _X Ni _aα V _bα M
n _{C α} Fe _{(1-abc) α} R _β, where R is at least one of B and Si, the range of X is 0 ≦ X ≦ 0.9, and the range of α is 1.5 ≦ α ≦ 2.5, and the range of β is 0 <β ≦
0.3, and the ranges of a, b, and c are 0.4 ≦ a ≦ 0.7,
The hydrogen storage alloy according to claim 1, wherein 0.1 ≦ b ≦ 0.3 and 0.1 ≦ c ≦ 0.32. 2. A hydrogen storage alloy electrode for an alkaline storage battery, characterized by using the hydrogen storage alloy according to claim 1.