JPH0426732A - Hydrogen storage ni-zr series alloy - Google Patents

Abstract

PURPOSE:To obtain a hydrogen storage Ni-Zr series alloy having an MgZn2, type crystalline structure and excellent in corrosion resistance in an alkaline electrolyte and hydrogen occluding-discharging capacity by specifying the compsn. constituted of Zr, Ti, Mn, Fe, Co, V and Ni. CONSTITUTION:This is a hydrogen storage Ni-Zr series alloy having a compsn. contg., by weight, 10 to 37% Zr, 5 to 25% Ti, 4 to 20% Mn, 0.01 to 5% Fe, 0.5 to 20% Co and 0.1 to 15% V, furthermore contg., at need, 1 to 7% Cu and/or 0.05 to 6% Cr and the balance Ni with inevitable impurities and having an MgZn2 type crystalline structure. The alloy is excellent in capacity and corrosion resistance in an alkaline electrolyte and suitable particularly for the use as the negative active substance of a closed type Ni-hydrogen storage battery.

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention is based on MgZn2 type crystal structure, that is, hexagonal C
The present invention relates to a hydrogen-absorbing Ni-Zr alloy having a type 14 crystal structure and particularly suitable for use as a negative electrode active material of a sealed N1 hydrogen storage battery.

[Conventional technology]

In general, a sealed N1-hydrogen storage battery is composed of a negative electrode using a hydrogen storage alloy as an active material, an Nj positive electrode, a separator, and an alkaline electrolyte, and the hydrogen storage alloy constituting the negative electrode contains ( 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 (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 Nl-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 N1-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 N1-hydrogen storage battery. % indicates weight%), Zr: 10-37%, Ti: 5-25%, Mn: 4
~20%, Fe: 0.01~5%, Co:
0.5-20%, V: 0.1-15%, further contains Cu: 1-7%, Cr: 0.05-6%, and the rest is N1. A hydrogen-absorbing Ni-Zr alloy with a composition consisting of unavoidable impurities has a M g Z n 2 type crystal structure (hexagonal C14 type crystal structure), and has a closed type N1 type crystal structure.
- A sealed type N that fully satisfies the properties (a) to (g) above required when used as a negative electrode active material in a hydrogen storage battery, and therefore uses it as a negative electrode active material.
1-Hydrogen storage batteries have large energy density and electric capacity, and have a long cycle life. They also have low self-discharge, excellent high-rate light and discharge characteristics, and are non-polluting and low-cost. The research results showed that it can exhibit 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: less than 5%, the desired effect cannot be obtained, while when the Zr content exceeds 37%,
There is no problem in terms of the dependence of the discharge capacity on the hydrogen dissociation pressure, but the hydrogen storage and desorption capacity begins to decline, and when the TI content exceeds 25%, the equilibrium hydrogen dissociation pressure increases to, for example, 5 atm or more. In order to ensure a large discharge capacity, a high hydrogen dissociation pressure is required, making it undesirable as a storage battery. : 5 to 25%.

(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 5%, the corrosion resistance will decrease, and if applied to a storage battery, self-discharge will progress, so the content should be reduced to 0.1%.
It was set at 1~5%.

(d)　C.

The Co component further increases hydrogen storage capacity and
When used as a negative electrode active material in i-hydrogen storage batteries, it has the effect of increasing the discharge capacity and significantly extending its service life, but if its content is less than 0.5%, the desired effect may not be achieved. No effect was obtained, while the content was 20
Even if the content exceeds 0.5%, no further improvement effect is seen due to the above action, so in consideration of economic efficiency, the content should be increased from 0.5% to 0.5%.
It was set at 20%.

(c) 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 to have as large an amount of hydrogen storage and release as possible. ■Ingredients have the effect of contributing to increasing the amount of hydrogen storage and release and optimizing the equilibrium hydrogen pressure, but if the content is less than 0.1%, the desired effect cannot be obtained. On the other hand, if its content exceeds 15%, 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 amount of hydrogen storage and release 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 action cannot be obtained, and on the other hand, if the content exceeds 7%, the amount of hydrogen storage and desorption will decrease, and the discharge capacity will decrease. 1-7%
It was determined that

(g) CrC component has the effect of further improving corrosion resistance in alkaline electrolyte without reducing hydrogen storage/release ability, so it is included as necessary, but its content is If the content is less than 0.05%, the desired effect of improving the above action cannot be obtained, while if the content exceeds 6%, the hydrogen storage and desorption ability will decrease.
It was set at 5-6%.

〔Example〕

Next, the hydrogen-absorbing Ni--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 in the range of
By setting the particle size to 0 mesh or less, both MgZ
Hydrogen storage alloys 1 to 20 of the present invention having a nz-type crystal structure,
Comparative hydrogen storage alloys 1 to 9 and conventional hydrogen storage alloys were each manufactured.

Next, various powdered hydrogen storage alloys obtained as a result are used as active materials, and a 2% aqueous solution of polyvinyl alcohol (PVA) is added thereto to form a paste, which has a porosity of 95%. It was filled into a commercially available Nj Iscar nonwoven fabric, dried, and further pressurized to give a flat size of 42
+++m x 35m+a, thickness: o, eo~
0.65 city shape (active material filling amount: approximately 2.8 g),
A negative electrode was manufactured by attaching an N1 thin plate as a lead to the negative side of this by welding, and on the other hand, two Ni sintered plates of the same size were prepared as positive electrodes, and these were placed on both sides of the negative electrode.
A sealed Nl-hydrogen storage battery was manufactured by charging an OH 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.

Moreover, the comparative hydrogen storage alloys 1 to 9 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 and discharging speed:
A charge/discharge test was conducted under the conditions of 0.2C, charge amount of electricity: 130% of the negative electrode capacity, one charge and discharge was one cycle, and after 10 cycles, 220 cycles, and 330
The discharge capacity after each cycle was measured.

Further, various powdered hydrogen storage alloys having the compositions shown in Table 1 were used, and the planar size was 90mm+
Same as the negative electrode plate of the storage battery used in the charge/discharge test above, except that the thickness was 40mm%, 0.60 to 0.85mm, and the capacity was 1450 to 500mAh (active material filling amount: about 6g). A negative electrode plate was manufactured under the following conditions, while a positive electrode plate was prepared by filling a Ni whisker nonwoven fabric with a porosity of 95% with nickel hydroxide [N j (OH) 2 ] as an active material, drying it, and then pressing it. , with the lead installed, plane dimensions: 70mm x 40rava, thickness: 0.65-0.70mm (capacity: 1000
~1050Ah), and the resulting negative and positive electrode plates are thinly wound with a separator in between, and placed in a case (this also serves as the ○ terminal) together with the electrolyte. This is a sealed Ni-hydrogen storage battery with a structure housed in. In addition, in this storage battery, the negative electrode capacity was made larger than the positive electrode capacity to constitute a positive electrode regulation storage battery.

In addition, the self-discharge test for these storage batteries involves first charging them at room temperature at 0.2C (200+nA) for 7 hours, then setting the temperature of the storage battery at 45℃ and placing it in a constant temperature oven in an open circuit state (no load is applied to the battery). After leaving it for one week and two weeks, take it out and heat it at room temperature at 0.2C (20
This was done by performing a discharge (0 mA) and determining the capacity remaining rate.

Furthermore, for various hydrogen storage alloys having the composition shown in Table 1, test pieces were cut out from the above ingot and embedded in plastic resin using a method generally called the l1uey test, and the corroded surface was removed. After polishing with emery paper #BUD, charge it into an Erlenmeyer flask with a cold finger type condenser.
An alkaline electrolyte corrosion test was conducted under the condition of holding in a boiling 30% KOH aqueous solution for 240 hours, and the corrosion weight loss after the test 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
0 exhibits superior corrosion resistance to alkaline electrolytes compared to conventional hydrogen storage alloys, and furthermore, when used as a negative electrode active material of a sealed Ni-hydrogen storage battery,
It is clear that storage batteries now have a high capacity, and compared to storage batteries using conventional hydrogen storage alloys, they show favorable results in that capacity loss is significantly smaller when repeated charge/discharge cycles are performed. As seen in Hydrogen Storage Alloys 1 to 9, when the content of any of the constituent components falls outside the scope of the present invention, the corrosion resistance to alkaline electrolytes and this It is clear that when used together with the negative electrode active material of a storage battery, the discharge capacity and/or self-discharge characteristics of the storage battery will be inferior.

As mentioned above, the hydrogen-absorbing Nl-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: 0.01-5%, Co: 0.5-2
0%, V: 0.1 to 15%, and the remainder is Ni and unavoidable impurities (weight%).
i-Zr alloy. (2) Zr: 10-37%, Ti: 5-25%, Mn:
4-20%, Fe: 0.01-5%, Co: 0.5-2
0%, V: 0.1 to 15%, and Cu: 1 to 7%, with the remainder consisting of Ni and unavoidable impurities (weight %). A hydrogen-absorbing Ni-Zr alloy with a MgZn_2 type crystal structure. (3) Zr: 10-37%, Ti: 5-25%, Mn:
4-20%, Fe: 0.01-5%, Co: 0.5-2
0%, V: 0.1 to 15%, further contains Cr: 0.05 to 6%, and the remainder is Ni and inevitable impurities (weight %). A hydrogen-absorbing Ni-Zr alloy with a MgZn_2 type crystal structure. (4) Zr: 10-37%, Ti: 5-25%, Mn:
4-20%, Fe: 0.01-5%, Co: 0.5-2
0%, V: 0.1 to 15%, and further contains Cu: 1 to 7%, Cr: 0.05 to 6%, and the remainder is Ni and unavoidable impurities. %) having a MgZn_2 type crystal structure.