JP2762669B2 - Hydrogen storage Ni-Zr alloy - Google Patents

Description

The present invention has a MgZn ₂ type crystal structure, that is, a hexagonal C14 type crystal structure, and is particularly suitable for use as a negative electrode active material of a sealed Ni-hydrogen storage battery. And a hydrogen storage Ni-Zr alloy.

[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 a hydrogen storage alloy constituting the negative electrode includes the following: a) Large hydrogen storage / release capability near room temperature.

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

(C) Corrosion resistance and durability (deterioration resistance) in an alkaline electrolyte.

(D) Hydrogen oxidation ability (catalysis) is large.

(E) Pulverization hardly occurs due to repeated storage and release of hydrogen.

(F) There is no (low) pollution.

(G) Low cost.

It is desired to have the above properties (a) to (g),
Furthermore, a sealed Ni-Hydrogen storage battery using a hydrogen storage alloy having such properties as an active material of a negative electrode has a large discharge capacity, a long charge / discharge cycle life, excellent rapid charge / discharge characteristics, and low self-charge characteristics. It is also well known that preferable performance such as discharge is exhibited.

Therefore, development of a hydrogen storage alloy particularly suitable for use as an active material constituting a negative electrode of a sealed Ni-hydrogen storage battery has been actively conducted, for example, MgZn type ₂ crystal described in JP-A-61-45563. Many hydrogen storage alloys have been proposed, including a hydrogen storage alloy having a structure, that is, a hexagonal C14 type crystal structure.

[Problems to be solved by the invention]

However, none of the hydrogen storage alloys already proposed satisfy all of the above properties required when used as a negative electrode active material of a sealed Ni-hydrogen storage battery, and further development is desired. It is the present situation.

[Means for solving the problem]

In view of the above, the present inventors have 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, and as a result, the weight% % Indicates weight%), Zr: 10-37%, Ti: 5-30%, Mn: 5-30%, Fe: 1-30%, Co: 0.5-20%, W: 0.01-15%, Al: 0.01 to 5%, and further, if necessary, Cu: 0.1 to 16%, Cr: 0.1 to 15%, with the balance being Ni and unavoidable impurities. The Zr-based alloy has a MgZn type ₂ crystal structure (hexagonal C1
(A) to (g) required when used as a negative electrode active material of a sealed Ni-hydrogen storage battery
The sealed Ni-Hydrogen storage battery using this as a negative electrode active material has a large energy density and electric capacity, has a long cycle life, and has a self-discharge property. The research results have shown that, in addition to the low charge and discharge characteristics, excellent performance can be achieved in combination with low pollution and low cost.

The present invention has been made based on the above research results, and the reason for limiting the component composition of the above-mentioned hydrogen-absorbing Ni-Zr-based alloy as described above will be described below.

(A) Zr and Ti These components not only provide the alloy with desirable hydrogen storage / release characteristics in the coexisting state, but also reduce the equilibrium hydrogen dissociation pressure (plateau pressure) at room temperature to, for example, 5 atm or less. However, its content is Zr: 10
% And Ti: less than 5%, the desired effect cannot be obtained. On the other hand, if the Zr content exceeds 37%, there is no problem in terms of the discharge capacity depending on the hydrogen dissociation pressure. When the release capacity decreases and the Ti content exceeds 30%, the equilibrium hydrogen dissociation pressure increases, for example, to 5 atmospheres or more, and in order to secure a large discharge capacity, a high hydrogen dissociation pressure is required. Is required as a storage battery, so that its content is Zr: 1
0 to 37%, Ti: 5 to 30%.

(B) Mn The Mn component improves hydrogen storage / release capability, improves the corrosion resistance and durability of the alloy in an alkaline electrolyte, and suppresses self-discharge when used as a negative electrode active material for storage batteries. However, if the content is less than 5%, the desired effect cannot be obtained, while the content is less than 30%.
%, The hydrogen storage / release characteristics are impaired, so the content was determined to be 5 to 30%.

(C) Fe The Fe component has the effect of further stabilizing hydrides, thereby contributing to the stabilization of storage battery performance, and the effect of Ni is impaired even when used as a partial substitute for Ni. However, if the content is less than 1%, the desired effect cannot be obtained, whereas if the content exceeds 30%, the hydrogen storage capacity is reduced. The content is 1
~ 30%.

(D) Co In the Co component, the hydrogen storage capacity is further increased,
-When used as a negative electrode active material of a hydrogen storage battery, it has an effect of increasing the discharge capacity and contributing to significantly prolonging the service life of the battery. However, if the content is less than 0.5%, a desired effect can be obtained in the above-mentioned effect. On the other hand, even if the content exceeds 20%, no further improvement effect is seen by the above-mentioned action, so that the content is set to 0.5 to 20% in consideration of economy.

(E) W The W component has the effect of further improving the corrosion resistance of the alloy in an alkaline electrolyte, improving the durability, and suppressing self-discharge in practical use as a negative electrode active material of a storage battery. If the content is less than 0.01%, the desired effect cannot be obtained in the above-mentioned action. On the other hand, if the content exceeds 15%, the hydrogen storage / release characteristics will be impaired. ~ 15%.

(F) Al The Al component has the effect of further improving the corrosion resistance of the alloy without deteriorating the ability to absorb and release hydrogen, thereby further suppressing self-discharge of the storage battery.
If the content is less than 5%, the desired effect cannot be obtained. If the content is more than 5%, the hydrogen storage / release ability will be remarkably reduced.
It was decided.

(G) Cu The Cu component has an effect of further increasing the amount of hydrogen occlusion and release and further optimizing the equilibrium hydrogen pressure. Therefore, the Cu component is contained as necessary. If the desired effect is not obtained, the content exceeds 7%. On the other hand, if the content exceeds 7%, the amount of hydrogen occlusion and release is reduced, and the discharge capacity is reduced. %.

(H) Cr The Cr component has an effect of further improving the corrosion resistance in the alkaline electrolyte without lowering the hydrogen absorbing / desorbing ability, and is contained as necessary. When the content is less than 15%, the desired effect of improving the effect cannot be obtained. On the other hand, when the content is more than 15%, the ability to absorb and release hydrogen is reduced.
It was set at 5%.

〔Example〕

Next, the hydrogen-absorbing Ni-Zr-based alloy of the present invention will be specifically described with reference to examples.

Using a normal high-frequency induction melting furnace, a molten Ni-Zr alloy having the component composition shown in Table 1 was prepared in an Ar atmosphere, and cast into a copper mold to form an ingot. In an Ar atmosphere, annealed at a predetermined temperature in the range of 900 to 1000 ° C. for 5 hours, then coarsely pulverized using a jaw crusher to coarse particles having a diameter of 2 mm or less, and further finely pulverized using a ball mill. By adjusting the particle size to 350 mesh or less, the hydrogen storage alloys 1 to 23 of the present invention, the comparative hydrogen storage alloys 1 to 10, and the conventional hydrogen storage alloys each having an MgZn ₂ type crystal structure were produced.

Then, various powdered hydrogen storage alloys obtained as a result are used as an active material. First, a 2% aqueous solution of polyvinyl alcohol (PVA) is added to the paste to form a paste, and the paste has a porosity of 95%. Filled into a commercially available Ni whisker non-woven fabric, dried, and further pressurized, planar dimensions: 42 mm x 35 m
m, thickness: 0.60-0.65mm (Active material filling: approx.
2.8 g), and a Ni thin plate serving as a lead is attached to one side of the negative electrode by welding to produce a negative electrode. On the other hand, two Ni sintered plates having the same dimensions as a positive electrode are prepared, and placed on both sides of the negative electrode.
A sealed Ni-hydrogen storage battery was manufactured by charging an aqueous solution of 0.1% KOH.

The resulting storage batteries were all open batteries, and the capacity of the negative electrode was easily measured by making the capacity of the positive electrode significantly larger than the capacity of the negative electrode.

Each of the comparative hydrogen storage alloys 1 to 10 has a composition in which the content of any one of the constituent components (marked with * in Table 1) is out of the range of the present invention.

Next, with respect to these various storage batteries, a charge / discharge test was performed under the conditions of a charge / discharge rate of 0.2 C and a charged amount of electricity: 130% of the negative electrode capacity.
The discharge capacity was measured after 0 cycles, after 220 cycles, and after 330 cycles.

Further, using various powdered hydrogen storage alloys having the compositions shown in Table 1, the plane size was 90 mm × 40 mm, the thickness was 0.60 to 0.65 mm, and the capacity was 1450 to 1500 mAh (active material filling amount: A negative plate was manufactured under the same conditions as the negative plate of the storage battery using the charge / discharge test described above, except that the weight was about 6 g). Filling nickel (Ni (OH) ₂ ) as an active material,
After drying and pressing further, attach the lead,
Plane dimensions: 70 mm x 40 mm, thickness: 0.65 to 0.70 mm (capacity: 1000 to 1050 mAh), and the resulting negative and positive plates were spirally wound through a separator. In this state, a sealed Ni-hydrogen storage battery having a structure housed in a case (also used as a terminal) together with the electrolytic solution was obtained. In addition, in this storage battery, the storage capacity of the positive electrode rule was configured by making the negative electrode capacity larger than the positive electrode capacity.

In the self-discharge test for these batteries, the batteries were charged at room temperature for 7 hours at 0.2 C (200 mA), and then the batteries were charged for 4 hours.
Leave it open for 1 week and 2 weeks in the open circuit condition (with no load on the battery) in a thermostat set at a temperature of 5 ° C.
After leaving, the battery was taken out, discharged at 0.2 C (200 mA) at room temperature, and the remaining capacity was determined.

Further, with respect to various hydrogen storage alloys having the component compositions shown in Table 1 as well, a test piece was cut out from the above ingot and embedded in a plastic resin using a method generally called a Huey test, and a corroded surface was formed. After being polished and finished with Emery Paper # 600, it was charged into a conical flask with a cold finger condenser and boiled.
An alkaline electrolyte corrosion test was carried out for 240 hours in a 30% KOH aqueous solution, and the corrosion loss after the test was measured. Table 1 shows the results of these measurements.

〔The invention's effect〕

From the results shown in Table 1, the hydrogen storage alloys of the present invention 1 to
No. 23 shows superior corrosion resistance to alkaline electrolyte compared to conventional hydrogen storage alloys, and when this is used as a negative electrode active material of a sealed Ni-hydrogen storage battery, the storage battery has a high capacity Thus, it is clear that the capacity decrease when the charge / discharge cycle is repeated is remarkably small as compared with the storage battery using the conventional hydrogen storage alloy, and it is clear that the comparative hydrogen storage alloys 1 to 10 show favorable results. As can be seen, even if the content of any of the constituents deviates from the scope of the present invention, compared to the hydrogen storage alloy of the present invention, the corrosion resistance to the alkaline electrolyte, and as a negative electrode active material of the storage battery It is clear that the characteristics of at least one of the discharge capacity and self-discharge of the storage battery when used are inferior.

As described above, the hydrogen storage Ni-Zr-based alloy of the present invention is:
In addition to having excellent corrosion resistance to alkaline electrolytes, and especially when used as a negative electrode active material for sealed Ni-Hydrogen batteries, it has all the characteristics required for the negative electrode active material in a state that fully satisfies it. This has industrially useful characteristics such as a significant reduction in self-discharge and a large discharge capacity over a long cycle life.

Claims (4)

(57) [Claims] [Claim 1] Zr: 10 to 37%, Ti: 5 to 30%, Mn: 5 to 30%, Fe: 1 to 30%, Co: 0.5 to 20%, W: 0.01 to 15%, Al: 0.01 A hydrogen-absorbing Ni-Zr-based alloy having a MgZn _2- type crystal structure, characterized in that the alloy contains Ni and inevitable impurities (the weight percentage being at least 5%). 2. Zr: 10 to 37%, Ti: 5 to 30%, Mn: 5 to 30%, Fe: 1 to 30%, Co: 0.5 to 20%, W: 0.01 to 15%, Al: 0.01 A MgZn type ₂ crystal structure characterized in that the composition contains Cu: 0.1 to 16%, and the balance has a composition (more than weight%) consisting of Ni and unavoidable impurities. Hydrogen storage Ni-Zr alloy. 3. Zr: 10 to 37%, Ti: 5 to 30%, Mn: 5 to 30%, Fe: 1 to 30%, Co: 0.5 to 20%, W: 0.01 to 15%, Al: 0.01 5%, containing further, Cr: 0.1 to 15%, containing, rest with MgZn ₂ type crystal structure and having a composition consisting of Ni and inevitable impurities (% by weight or more) Hydrogen storage Ni-Zr alloy. 4. Zr: 10 to 37%, Ti: 5 to 30%, Mn: 5 to 30%, Fe: 1 to 30%, Co: 0.5 to 20%, W: 0.01 to 15%, Al: 0.01 MgZn, characterized in that the composition further comprises: Cu: 0.1 to 16%, Cr: 0.1 to 15%, and the balance is composed of Ni and unavoidable impurities (more than weight%). A hydrogen-absorbing Ni-Zr alloy with a type ₂ crystal structure.