JP3188780B2 - 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 JP-A-51-13934) have the advantage that they have a large hydrogen storage capacity, but they are susceptible to corrosion by alkali solutions and acid solutions, and are therefore liable to be pulverized and expensive La metal. there were.

[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 still short, and its performance is still insufficient.

Further, the alkaline storage battery using a LaNi5 alloy or an improved alloy thereof as a negative electrode has a disadvantage that when used at a high temperature of 50 ° C. or more, the electric capacity is significantly reduced, and the capacity is not sufficiently recovered even after returning to room temperature. was there.
The mixture of La-Ce-Pr-Nd is generally known as a misch metal (abbreviated as Mm). The present inventors studied the influence of the amount of carbon contained in the hydrogen storage alloy, and found that the carbon content was 100 ppm or more and 500 ppm or more.
ppm or less, and when the composition of the alloy to be used is a specific one, the corrosiveness of the hydrogen storage alloy is greatly improved, and that 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 high capacity recovery rate when used at a high temperature of 50 ° C. or higher and returned to room temperature.

[0007]

Means for Solving the Problems The above various objects of the present invention, together with the carbon content is 100ppm or 500ppm or less, the general formula _{Ln a Ni 5- (b + c} + d) Co b Al
was achieved by the hydrogen absorbing alloy is characterized by being represented by _c M _d. Ln in the above general formula is 40 to 80% by weight.
La, 10-60 wt% Ce, 5 wt% or less Pr
And a metal having a composition consisting of 5% by weight or less of Nd.
n, at least one element selected from Fe and Cu, a is 0.95 ≦ a ≦ 1.05, and b is 0.
2 ≦ b ≦ 1.0, c is 0.1 ≦ c ≦ 1.0, d is 0 ≦ d
Represents a rational number of ≦ 0.5.

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 Al c M d
Is positioned as an improved type of LaNi ₅ . That is, Ln is at least La and C
e is a rare earth element having a composition consisting of
In particular, La is 40 to 80% by weight, Ce is 10 to 60% by weight.
It is preferred that When La exceeds 80% by weight, L
Similar to ANI ₅ alloy, when it is it a negative electrode, cost becomes disadvantageous with charge-discharge cycle life of the alkaline storage battery is extremely short, it is less than 40% by weight, the hydrogen storage capacity is insufficient Become.

As elements other than La and Ce, in particular, P
When r is 5% by weight or less, preferably 1% by weight or less and Nd is 5% by weight or less , preferably 1% by weight or less , it is particularly suitable as an electrode for an alkaline storage battery. It is preferable to add at least 0.1% by weight of Pr and Nd. 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. The feature of the hydrogen storage alloy of the present invention is that, together with the composition of the alloy , 100 ppm in the hydrogen storage alloy
The point is that carbon of at least 500 ppm is added.

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 100 p.
If it is as small as pm or more and 500 ppm or less, 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. On the other hand, 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, It is believed to promote corrosion.

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, Ln _a Ni added with fewer carbon 500ppm by methods known
To produce a _{5- (b + c + d)} Co b Al c M d of the alloy,
Next, it can be easily obtained by adding and dissolving the carbon inactivating metal in an amount of three times or less the equivalent of the carbon contained. 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 long cycle life when repeated charging and discharging,
It has a high capacity recovery rate when used at a high temperature of 50 ° C. or higher and returned to use at room temperature.

[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 1-19. 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 to inactivate the carbon as appropriate, it 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. After charging the obtained battery for 2 hours at a current of 40 mA, the battery was repeatedly charged and discharged at a current of 20 mA until the battery voltage reached 0.6 V. The cycle life at 20 ° C. was examined, and the temperature was raised to 50 ° C. After raising 2
The recovery rate of the capacity when returned to 0 ° C. was also examined. Table 3 shows the results.

Comparative Examples 1 to 12 In the same manner as in the examples, samples in which Pr and Nd in the alloy each exceeded 5% by weight were prepared (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 100 ppm or more and 500 ppm or less,
The capacity storage rate was as good as 85% or more. When Pr and Nd, which are the rare earth element composition components in the alloy, do not exceed 5% by weight, the capacity recovery rate is as good as 85% by weight or more. Further, it has been proved that an inert carbon compound containing a metal for inactivating carbon is further improved.

Continuation of 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-4-253158 (JP, A) JP 1987-19864 (JP, A) JP-A-5-156395 (JP, A) JP-A-3-294444 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C22C 1 / 00-49/14 H01M 4/38 H01M 4/24-4/26

Claims (3)

(57) [Claims] 1. A carbon content of 100 ppm or more and 500 ppm or more.
with ppm or less, the general formula _{Ln a Ni 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 of 40 to 80 wt% L
a, a metal having a composition of 10 to 60% by weight of Ce, 5% by weight or less of Pr and 5% by weight or less of Nd, M is Mn, F
It represents at least one element selected from e and Cu, and ad 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. The method according to claim 1, wherein the amount of Si,
The hydrogen storage alloy according to claim 1, wherein the hydrogen storage alloy contains at least one element selected from the group consisting of Ti, Zr, Ta, Nb, and V. 3. An electrode for an alkaline storage battery comprising the hydrogen storage alloy according to claim 1 or 2.