JP3095101B2 - Hydrogen storage alloy and electrode using the same - Google Patents

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 more particularly to a hydrogen storage alloy suitable as an electrode for an alkaline storage battery and an electrode using the same.

[0002]

2. Description of the Related Art Since the discovery of a hydrogen storage alloy that absorbs and releases hydrogen, its application has been expanded not only to hydrogen storage means but also to heat pumps and batteries. In particular, alkaline storage batteries using a hydrogen storage alloy as a negative electrode have almost reached practical use, and the hydrogen storage alloy used has been continuously improved. That is, the LaNi ₅ initially studied
Alloys (see Japanese Patent Application Laid-Open No. 51-13934) have the advantage of a large hydrogen storage capacity. On the other hand, La metal is expensive, and is easily pulverized by repeated storage and release of hydrogen. There was a drawback that the solution was easily corroded.

[0003] The disadvantage is that a part of La is made of Ce, P
By substituting r, Nd and other rare earth elements,
And / or by replacing a part of Ni with a metal such as Co, Al, Mn (for example,
048918, 54-0664014, 60-2
Nos. 50558, 61-233969 and 62-4
No. 3064).

[0004] Although these improved alloys have a slightly reduced hydrogen storage capacity as compared with the LaNi ₅ alloy, they have improved corrosion resistance to alkali solutions and acid solutions, and when used as electrodes, charge and discharge of alkaline storage batteries. The cycle life can be extended. However, from an industrial point of view, the charge / discharge cycle life is short, the electric capacity is not sufficient, and the performance is still insufficient.

[0005] The mixture of La-Ce-Pr-Nd is
It is generally known as misch metal (abbreviated as Mm). The present inventors studied the effect of the amount of carbon contained in the hydrogen storage alloy, and found that the amount of added carbon was 30 ppm.
When the composition of the alloy used is set to a specific value, the corrosion resistance of the hydrogen storage alloy is greatly improved, and it is particularly suitable as a negative electrode for an alkaline battery. The present invention has been found.

[0006]

SUMMARY OF THE INVENTION Accordingly, a first object of the present invention is to provide a long-life hydrogen storage alloy which has high corrosion resistance and is suppressed from being pulverized when used for hydrogen storage or a heat pump. Is to do. A second object of the present invention is to
An object of the present invention is to provide a hydrogen storage alloy suitable as a negative electrode of an alkaline storage battery. A third object of the present invention is to provide an electrode for an alkaline storage battery comprising a hydrogen storage alloy having a long charge and discharge cycle life. Further, a fourth object of the present invention is to provide an electrode for an alkaline storage battery comprising a hydrogen storage alloy having a large electric capacity.

[0007]

Above the objectives of the present invention SUMMARY OF], along with the added amount of carbon is 30 ppm to 500 ppm, in the general formula _{Lna Ni 5- (b + c +} d) Co b Al c M d Achieved by a hydrogen storage alloy characterized by being represented. Ln in the above general formula is 40 to 80% by weight of La,
A metal having a composition of 10 to 60 wt% Pr, 5 wt% or less Nd and 5 wt% or less Ce, M represents at least one element selected from Mn, Fe and Cu, and a represents 0 .95 ≦ a ≦ 1.05, b is 0.2 ≦ b ≦
1.0, c is 0.1 ≦ c ≦ 1.0, d is 0 ≦ d ≦ 0.5
Represents the rational number of.

Hereinafter, the present invention will be described in detail. Formula for use in the present invention _{Ln a Ni 5- (b + c} + d) Co b A
hydrogen absorbing alloy represented by l _c M _d is positioned as a variant of LaNi _5. That is, Ln is at least L
a rare earth element having a composition of a and Pr. From a practical viewpoint, particularly, La is 40 to 80% by weight, and Pr is 10 to 6% by weight.
It is preferably 0% by weight. When La exceeds 80% by weight, similar to LaNi ₅ alloy, when it is used as a negative electrode, the cycle life of charging and discharging of the alkaline storage battery becomes extremely short and disadvantageous in cost. In addition, the hydrogen storage amount becomes insufficient.

As elements other than La and Pr, in particular, N
When d is 5% by weight or less, preferably 1% by weight or less and Ce is 5% by weight or less , preferably 1% by weight or less , it is particularly suitable as an electrode for an alkaline storage battery. Nd and Ce are preferably added at least 0.1% by weight. Further, Co, Al and M each have an action of imparting corrosion resistance to the hydrogen storage alloy. The content b of Co is 0.2 ≦ b ≦ 1.0, particularly 0.5 ≦ b ≦
It is preferred to be in the range of 1.0. Al content c
Is 0.1 ≦ c ≦ 1.0, and in particular, 0.2 ≦ c ≦
It is preferably 0.5.

[0010] M is at least one element selected from Mn, Fe and Cu, and is particularly preferably Mn and / or Cu. The content d is 0
≦ d ≦ 0.5, and particularly preferably 0.1 ≦ d ≦ 0.3. A feature of the hydrogen storage alloy of the present invention is that the hydrogen storage alloy contains 500 ppm or less of carbon in the hydrogen storage alloy together with the composition of the alloy.

Although the mechanism of action of carbon in the hydrogen storage alloy is not always clear, it can be estimated as follows.
That is, the carbon added to the hydrogen storage alloy usually precipitates at the alloy grain boundaries. In this case, the amount of added carbon is 30 pp.
When the amount is as small as m to 500 ppm, carbon slightly precipitated at the grain boundary forms a film, and the film functions as a protective film against an alkali solution or an acid solution. In order for the carbon film to function as a protective film, the amount of carbon added is preferably 50 ppm to 50 ppm .
Preferably it is 500 ppm . As the amount of carbon added increases to 500 ppm or more, the carbon film formed at the grain boundaries becomes thicker, which not only hinders the absorption and release of hydrogen, but also causes excess carbon to react with hydrogen and cause corrosion. It is thought to promote.

In the present invention, Nb, Si, T
a, at least one element of Ti, V and Zr,
It is preferable that these elements be added in an amount equal to or less than 3 times the equivalent of carbon because these elements react with carbon slightly precipitated at the grain boundaries to form inert carbon compounds, and thus the grain boundaries are reduced. It is considered that the inert film formed in the above further improves the corrosion resistance to an alkali solution or an acid solution. Therefore, the amount of the above-mentioned metal used is not more than three times the equivalent of the contained carbon.

[0013] Hydrogen storage alloys of the present invention is to produce a _{Ln a Ni 5- (b + c} + d) of Co _b Al _c M _d alloy by a known method, then the equivalent amount of carbon contained 3 Less than twice the amount,
It can be easily obtained by adding and dissolving the carbon inactivating metal. An electrode can be easily formed by shaping using a known binder.
The alkaline storage battery using the hydrogen storage alloy of the present invention as a negative electrode has a large electric capacity and a long cycle life even after repeated charging and discharging.

[0014]

The hydrogen storage alloy of the present invention is inexpensive because misch metal can be used. In addition, since a very small amount of carbon is contained, the corrosiveness is greatly improved, and it is not only difficult to pulverize even if hydrogen is repeatedly absorbed and released, but also has a high corrosion resistance to an alkali solution or an acid solution. It is suitable as a negative electrode for a storage battery.

[0015]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the present invention is limited thereto.

Embodiments 1 to 21. La (purity 99% or more), Ce (purity 99% or more), Pr (purity 99% or more), Nd (purity 99% or more), two types of misch metal Lm (La 61%, Ce 8%, Pr 24%, Nd7
%) And Mm (La 25%, Ce 50%, Pr 10%,
Nd 15%), Ni (purity 99% or more), Co (purity 9)
9% or more), Al (99% or more purity) and M (Mn, F
e, Cu) were weighed and mixed so as to have a predetermined composition. In addition, carbon is
After adding a metal for inactivating carbon, the mixture was heated and melted by an arc melting method to produce a hydrogen storage alloy having the composition shown in Table 1.

[0017]

[Table 1]

The obtained alloy was pulverized to a powder having a particle size of 75 μm or less. 2.5 g of a 3% by weight aqueous solution of polyvinyl alcohol is mixed with 10 g of the powder to form a paste. The paste is filled in a foamed nickel metal porous body, dried, and then pressed and molded to a thickness. 0.5
A negative electrode having a thickness of about 1.0 mm was manufactured, and then a lead wire was attached to form a negative electrode. As the positive electrode, a porous nickel sintered body is impregnated with Ni (OH) ₂ , which is subjected to a chemical conversion treatment, and
An iOOH electrode was fabricated.

The above-described negative electrode and positive electrode were bonded via a polyolefin nonwoven fabric separator, and a battery was formed using 6 mol / liter KOH as an electrolytic solution. The obtained battery was charged with a current of 40 mA for 2 hours, and then repeatedly charged and discharged at a current of 20 mA until the battery voltage reached 0.6 V, and the cycle life at 20 ° C. was examined.

Comparative Examples 1 to 12 In the same manner as in the examples, samples in which Ce and Nd in the alloy each exceeded 5% by weight were produced (Table 2), and the same tests as in the examples were performed. The results are as shown in Table 3.

[0021]

[Table 2]

[0022]

[Table 3]

As is clear from the results in Table 3, when the amount of carbon in the alloy is 500 ppm or less, the capacity storage rate is 85%.
% Or more. When Nd and Ce, which are rare earth element components in the alloy, do not exceed 5% by weight,
The result was that the capacity was large. Further, it has been proved that an inert carbon compound containing a metal for inactivating carbon is further improved.

Continuation of the front page (72) Inventor Shigenobu Tajima 2-5-1-5 Kitafu, Takefu-shi, Fukui Shin-Etsu Chemical Co., Ltd. Magnetic Materials Research Laboratory (56) References JP-A-60-43451 (JP, A) Hei 4-190558 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C22C 19/00 C22C 19/03 H01M 4/38

Claims (3)

(57) [Claims] 1. The amount of carbon added is 30 ppm to 500 pp.
m or less and the general formula LnaNi _{5- (b + c + d)} Co
_b Al _c M hydrogen absorbing alloy is characterized by being represented by _d; however, the Ln in the general formula 40 to 80 wt% of La,
M is a metal having a composition of 10 to 60% by weight of Pr, 5% by weight or less of Nd and 5% by weight or less of Ce, and M represents at least one element selected from Mn, Fe, and Cu. Represents a rational number in the following range. 0.95 ≦ a ≦ 1.05 0.2 ≦ b ≦ 1.0 0.1 ≦ c ≦ 1.0 0 ≦ d ≦ 0.5 2. Nb, not more than 3 times the equivalent of carbon.
The hydrogen storage alloy according to claim 1, wherein the hydrogen storage alloy contains at least one element selected from the group consisting of Si, Ti, Ta, V, and Zr. 3. An electrode for an alkaline storage battery using the hydrogen storage alloy according to claim 1 or 2 .