JPH0466633A - Hydrogen storage ni-zr series alloy - Google Patents

Abstract

PURPOSE:To offer a hydrogen storage alloy, excellent in corrosion resistance to an alkaline electrolyte, decreasing the self-discharge of a storage battery and securing a high discharging capacity over a long cycle life by limiting the compsn. of an Ni-Zr series alloy. CONSTITUTION:The above alloy having a compsn. contg., by weight, 10 to 37% Zr, 5 to 25% Ti, 4 to 20% Mn, 0.01 to 15% Fe, 0.001 to 0.5% Pt or Au, 0.1 to 15% V and the balance Ni with inevitable impurities and having and MgZn2 type crystalline structure is prepd. If required, 1 to 7% Cu and/or 0.05 to 7% Cr is added to the above compsn. In this way, this alloy has excellent corrosion resistance to an alkaline electrolyte, decreases the self-discharge of a storage battery when it is used particularly as the active material in the negative pole in a closed Ni-hydrogen storage battery, and can furthermore secure a high discharging capacity over long cycle life.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is directed to MgZn having a 2-type crystal structure, that is, a hexagonal C14-type crystal structure, and which is particularly suitable for use as a negative electrode active material of a sealed Ni-hydrogen storage battery. Hydrogen storage Ni suitable for
-This relates to Zr-based alloys.

[Conventional technology]

Generally, a sealed Ni-hydrogen storage battery is composed of a negative electrode using a hydrogen storage alloy as an active material, a Ni positive electrode, a separator, and an alkaline electrolyte, and the hydrogen storage alloy constituting the negative electrode includes: a) High hydrogen absorption and release ability near room temperature.

(b) The equilibrium hydrogen dissociation pressure corresponding to the plateau pressure at a temperature near room temperature in the PCT curve is relatively low (A (5 atm or less).

(C) Corrosion resistance and durability (deterioration resistance) in alkaline electrolytes.

(d) High hydrogen oxidation ability (catalytic action).

(e) Pulverization due to repeated absorption and release of hydrogen is unlikely to occur.

(f) No (low) pollution.

(g) It is low cost.

A sealed Ni-hydrogen storage battery is desired to have the properties (a) to (g) above, and further uses a hydrogen storage alloy having such properties as the active material of the negative electrode.
It is also well known that they exhibit favorable performances such as large discharge capacity, long charge/discharge cycle life, excellent rapid light/discharge characteristics, and low self-discharge.

Therefore, the development of hydrogen storage alloys particularly suitable for use as active materials constituting the negative electrode of sealed Ni-hydrogen storage batteries has been actively carried out.
A large number of hydrogen storage alloys have been proposed, including a hydrogen storage alloy having a M g Z n 2 type crystal structure, that is, a hexagonal C14 type crystal structure, described in the above publication.

[Problem to be solved by the invention]

However, none of the hydrogen storage alloys that have already been proposed satisfies all of the above properties required for use as negative electrode active materials in sealed Ni-hydrogen storage batteries, and further development is desired. The current situation is that

[Means to solve the problem]

Therefore, from the above-mentioned viewpoint, the present inventors conducted research to develop a hydrogen storage alloy particularly suitable for use as a negative electrode active material of a sealed Ni-hydrogen storage battery. % indicates weight %), Zr: IO ~ 37%, Ti: 5 ~ 25%, Mn:
4-20%, Fe: 0.01-15%, P
t or Au: 0.001-0.5%, ■: 0°1
~15%, and further contains one or two of Cu: 1~7%, Cr: 0.05~7%, as necessary, and the rest consists of Ni and inevitable impurities. The hydrogen storage Ni-Zr alloy having the composition M
gZn has a 2-type crystal structure (hexagonal C14-type crystal structure) and fully satisfies the above properties (a) to (g) required when used as a negative electrode active material of a sealed Ni-hydrogen storage battery. Therefore, a sealed Ni--hydrogen storage battery using this as the negative electrode active material has high energy density and electric capacity, and has a long cycle life. Research has shown that it has excellent discharge characteristics, is non-polluting and low cost, and exhibits excellent performance.

This invention has been made based on the above research results, and the reason why the composition of the hydrogen storage Ni-Zr alloy is limited as described above will be explained below.

(a) Zr and Ti These components, when coexisting, provide the alloy with desirable hydrogen storage and desorption properties, and also have the effect of lowering the equilibrium hydrogen dissociation pressure (plateau pressure) at room temperature to, for example, 5 atm or less. However, the content is Zr:1
When the Zr content is less than 0% and Ti is less than 5%, the desired effect cannot be obtained, while when the Zr content exceeds 37%, there is no problem in terms of the hydrogen dissociation pressure dependence of the discharge capacity, but the hydrogen absorption・If the release capacity decreases and the Ti content exceeds 25%, the equilibrium hydrogen dissociation pressure will rise to, for example, 5 atm or more, and in order to secure a large discharge capacity, high hydrogen dissociation is required. Since this requires pressure and is not desirable as a storage battery, the contents were determined to be Zr: 10-37% and Ti: 5-25%, respectively.

(b) Mn The Mn component not only improves hydrogen storage and release ability, but also improves the corrosion resistance and durability of the alloy in alkaline electrolytes, and suppresses self-discharge when used as a negative electrode active material in storage batteries. However, if its content is less than 4%, the desired effect cannot be obtained; on the other hand, if its content is less than 2%,
If it exceeds 0%, the hydrogen storage and release characteristics will be impaired, so the content was set at 4 to 20%.

(c) Fe The Fe component has the effect of sizing the formed powder during powdering when used as a negative electrode active material of a storage battery, but if its content is less than 0.01%, the above effect will not be achieved. If the desired effect is not obtained, and if the content exceeds 15%, the corrosion resistance will decrease, and when applied to a storage battery, self-discharge will progress, so the content should be reduced to 0.
．． It was set at 01-15%.

(d) Pt or Au These components further increase the hydrogen storage capacity, thereby increasing the discharge capacity when used as the negative electrode active material of a Ni-hydrogen storage battery, contributing to a significant extension of its service life. However, the content is 0.0
If the content is less than 0.01%, the desired effect cannot be obtained in the above action, and even if the content exceeds 0.5% on each side, the effect of further improving the action cannot be obtained. The amounts were determined to be 0.001 to 0.596, respectively.

(e) V As mentioned above, it is desirable for a sealed Ni-hydrogen storage battery to have an equilibrium hydrogen dissociation pressure at room temperature that is not excessively high (for example, 5 atm or less) and a hydrogen storage/release capacity that is as large as possible. ■The component has the effect of contributing to increasing the hydrogen storage/desorption capacity and optimizing the equilibrium hydrogen pressure, but if the content is less than 0.1%, the desired effect will not be achieved. On the other hand, if the content exceeds 5%, the equilibrium hydrogen pressure will become too high, and it will dissolve into the electrolyte, promoting self-discharge. .1 to 15%.

(f') Cu The Cu component has the effect of further increasing the hydrogen storage/desorption capacity and optimizing the equilibrium hydrogen pressure, so it is included as necessary, but if the content is less than 1%, The desired effect of improving the above-mentioned action cannot be obtained, and on the other hand, if the content exceeds 7%, the hydrogen absorption/desorption ability will decrease and the discharge capacity will decrease. It was set at 7%.

(g) Cr The Cr component has the effect of further improving corrosion resistance in an alkaline electrolyte without reducing the hydrogen absorption/desorption ability, so it is included as necessary, but if the content is 0. If the content is less than 0.05%, the desired effect of improving the above action cannot be obtained, while if the content exceeds 7%, the hydrogen storage and desorption ability will decrease.
It was set at 5-7%.

〔Example〕

Next, the hydrogen storage N1-Zr alloy of the present invention will be specifically explained with reference to Examples.

Molten Ni-Zr alloys having the compositions shown in Table 1 are prepared in an Ar atmosphere using a conventional high-frequency induction melting furnace, and cast into a copper mold to form an ingot. 900-1000℃ in Ar atmosphere
Annealed at a predetermined temperature within the range of 5 hours, then coarsely crushed using a show crusher to obtain coarse particles with a diameter of 22 mm or less, and then finely crushed using a ball mill.
Both M
Hydrogen storage alloys 1 to 22 of the present invention, comparative hydrogen storage alloys 1 to 10, and conventional hydrogen storage alloys each having a g Z n Z-type crystal structure were manufactured.

Next, using the resulting various powdered hydrogen storage alloys as active materials, first, a 2% aqueous solution of polyvinyl alcohol (PVA) was added thereto to form a paste, which had a porosity of 95%. A commercially available Ni whisker nonwoven fabric was filled, dried, and further pressurized to obtain a planar size of 42
mm x 35mm, thickness: 0. BO~0.6
A negative electrode was manufactured by attaching a Ni thin plate to the negative side of the negative electrode by welding to the negative side of the negative electrode, and two Ni sintered plates of the same size were prepared as positive electrodes. This was placed on both sides of the negative electrode, and 30% KOH
A sealed NI'-hydrogen storage battery was manufactured by charging an aqueous solution.

The various storage batteries obtained as a result were all open batteries, and the capacity of the positive electrode was made significantly larger than the capacity of the negative electrode, thereby making it easier to measure the capacity of the negative electrode.

In addition, the comparative hydrogen storage alloys 1 to IO all have compositions in which the content of one of the constituent components (marked with * in Table 1) is outside the scope of the present invention.

Next, for these various storage batteries, the charging/discharging speed 7
A charge/discharge test was conducted under the conditions of 0.2C, charging electric Ti: 130% of the negative electrode capacity, one charge and discharge was considered as one cycle, and the discharge capacity after 140 cycles, 280 cycles, and 420 cycles was calculated. Each was measured.

In addition, various powdered hydrogen storage alloys having the compositions shown in Table 1 were used, and the planar size was 90 mm x 40 m.
ms thickness: 0.60~0.65mm, capacity: 1
The negative electrode plate was manufactured under the same conditions as the negative electrode plate of the storage battery used in the above charging/discharging test, except that the charge was 450 to 1500 mAh (active material filling amount: approximately 6 g), while the positive electrode plate was manufactured at 95%
A Ni whisker nonwoven fabric with a porosity of =0.65~0.
70mm shape (capacity: 1000-105010
5O, and the resulting negative electrode plate and positive electrode plate are housed in a case (which also serves as the ○ terminal) together with the electrolyte in a spiral shape with a separator in between. It was a sealed N1-hydrogen storage battery. In addition,
In this storage battery, the negative electrode capacity was larger than the positive electrode capacity to constitute a positive electrode regulation storage battery.

In addition, in the self-discharge test for these storage batteries, first charge them at room temperature at 0.2C (20DIIA) for 7 hours, then set the temperature of the storage battery at 45℃ and place it in a constant temperature oven in an open circuit state (no load is applied to the battery). condition) for 240 hours and 480 hours, after which it was taken out and 0.2
This was performed by discharging at 20 hA and determining the remaining capacity.

Furthermore, using a method generally called the Huey test, test pieces were cut from the above ingot and embedded in plastic resin for various hydrogen storage alloys having the compositions shown in Table 1. After polishing with Emery Vapor #600, it was charged into an Erlenmeyer flask with a cold finger type condenser, and an alkaline electrolyte corrosion test was conducted under the conditions of holding it in a boiling 35% KOH aqueous solution for 120 hours. Weight loss was measured. The results of these measurements are shown in Table 1.

〔Effect of the invention〕

From the results shown in Table 1, hydrogen storage alloys 1 to 2 of the present invention
2 exhibits superior corrosion resistance to alkaline electrolytes compared to conventional hydrogen storage alloys, and furthermore, when used as the negative electrode active material of a sealed Ni-hydrogen storage battery, the storage battery has a high capacity. It is clear that compared to storage batteries using conventional hydrogen storage alloys, the capacity decrease is significantly smaller when repeated charge/discharge cycles are performed, which is a favorable result.On the other hand, comparative hydrogen storage alloys 1 to IO
As can be seen in the figure, if the content of any of the constituent components is outside the scope of the present invention, the corrosion resistance to alkaline electrolytes and the corrosion resistance of the hydrogen storage alloy of the present invention may be lower than that of the hydrogen storage alloy of the present invention. It is clear that when used as a storage battery, the discharge capacity and/or self-discharge characteristics of the storage battery become inferior.

As mentioned above, the hydrogen-absorbing Ni-Zr alloy of the present invention has excellent corrosion resistance against alkaline electrolytes, and
In particular, when used as a negative electrode active material in a sealed Ni-Hydrogen storage battery, it fully satisfies all of the characteristics required for a negative electrode active material, significantly reducing self-discharge of the storage battery and resulting in a longer cycle time. It has industrially useful characteristics such as ensuring a large discharge capacity over its lifetime.

Claims (4)

[Claims] (1) Zr: 10-37%, Ti: 5-25%, Mn:
4-20%, Fe: 0.01-15%, Pt or Au
: 0.001 to 0.5%, V: 0.1 to 15%, and the remainder is Ni and unavoidable impurities (weight %). Hydrogen storage Ni-Zr alloy. (2) Zr: 10-37%, Ti: 5-25%, Mn:
4-20%, Fe: 0.01-15%, Pt or Au
: 0.001 to 0.5%, V: 0.1 to 15%, further contains Cu: 1 to 7%, and the remainder is Ni and unavoidable impurities (wt%) A hydrogen-absorbing Ni-Zr alloy having a MgZn_2 type crystal structure. (3) Zr: 10-37%, Ti: 5-25%, Mn:
4-20%, Fe: 0.01-15%, Pt or Au
Cr: 0.001 to 0.5%, V: 0.1 to 15%, and Cr: 0.05 to 7%, with the remainder being Ni and unavoidable impurities (by weight) %) having a MgZn_2 type crystal structure. (4) Zr: 10-37%, Ti: 5-25%, Mn:
4-20%, Fe: 0.01-15%, Pt or Au
:0.001~0.5%, V:0.1~15%, and further contains Cu:1~7%, Cr:0.05~7%, and the rest is Ni and unavoidable. A hydrogen-absorbing Ni-Zr alloy having a MgZn_2 type crystal structure characterized by having a composition (the above weight %) consisting of impurities.