JPH11217641A - Hydrogen storage alloy - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an alloy suitable for a cathode for Ni-hydrogen battery effective at a low temp. by containing a specified compound as well as a specified Mg. SOLUTION: A formula shows the compound used. In the formula, R shows a mixture consisting of >=77 wt.% La and <=23 wt.% one kind or more of rare earth metals except La. M shows one kind or more of metals selected from a group of Fe, Cr, Cu, Mn. (a)-(b) are a positive number showing a mol ratio for R and are shown in 30 <=a<=4.5; 0.3<=b<=1.0; 0<=c<=0.6; 0<=d<=0.5, the alloy contains 50-500 ppm Mg, further <=0.05 wt.% Ti, <=0.05 wt.% Pb, <=0.3 wt.% O, <=0.05 wt.% C and preferably <=0.05 wt.% S, by this method, a negative pole which has a high capacity a well as a long cycle life and is excellent in a high rate discharge property, a low temp. discharge property resoling from effect of a minute quantity of an eddying element of Mg, etc., is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a hydrogen storage alloy, and more particularly to a hydrogen storage alloy suitable for use as a negative electrode of an alkaline storage battery.

[0002]

2. Description of the Related Art Since the discovery of a hydrogen storage alloy that stores and releases hydrogen, its application has been extended to heat pumps and batteries as well as simple hydrogen storage means. In recent years, with the development of electronic technology, miniaturization and labor saving of electronic devices have become important factors. further,
Recently, storage batteries using such alloys have been used in high altitude or cold areas, and batteries with excellent low-temperature characteristics have been eagerly desired.

In particular, an alkaline storage battery using a hydrogen storage alloy as a negative electrode has been put to practical use, and the hydrogen storage alloy used has been continuously improved. The LaNi5 alloy initially studied (see JP-A-51-13934) has the advantage that it has a large hydrogen storage capacity, but is liable to be pulverized by repeated storage and release of hydrogen, thereby increasing the specific surface area of the alloy surface. However, there is a disadvantage that the deteriorated area increases, and furthermore, it is easily corroded by an alkali solution or an acid solution.

The disadvantage is that a part of La is made of Ce, Pr,
By substituting Nd and other rare earth metal elements,
And / or by replacing a part of Ni with a metal such as Co, Al, Mn (for example,
48918, 54-64014, 60
-250558, 61-233968,
No. 62-43064). As an alloy in which a part of La is replaced by Ce or the like, misch metal (Mm) containing about 40 to 50% by weight of Ce or La
L containing about 60% by weight and about 10 to 30% by weight of Ce
a Rich misch metal (Lm) is used.

[0005]

SUMMARY OF THE INVENTION Generally, for batteries,
When a La-Ni-based hydrogen storage alloy is used, it is important that the battery has high capacity, good discharge characteristics at a lower temperature, and a long charge / discharge cycle life. Then, La is partially replaced with Ce to achieve the purpose. In the above-mentioned conventional technology, the charge / discharge cycle life is improved, but the high-rate discharge characteristics and the life at low temperatures are not improved. Also,
It has been found that replacing the Ni side with Co, Mn, Al, or the like exerts the effects of high-rate discharge characteristics at normal temperature and life. Accordingly, an object of the present invention is to provide an effective N
An object of the present invention is to provide a hydrogen storage alloy suitable as a negative electrode for an i-hydrogen storage battery.

[0006]

Means for Solving the Problems Accordingly, the present inventors have
As a result of repeatedly examining the synergistic action on the La side and the Ni side,
The La content on the La side is made a certain amount or more, and the addition effect of a trace metal element such as Mg and the addition effect of non-metal elements such as carbon and oxygen provide a high capacity at a low temperature and a high rate discharge characteristic and discharge characteristic. It has been found that a hydrogen storage alloy suitable for a negative electrode of an alkaline storage battery having good cycle life and good cycle life is obtained, and the present invention has been achieved.

The present invention relates to a La—Ni-based hydrogen storage alloy, wherein the content of Mg in the hydrogen storage alloy is 50 to 50.
0 ppm and the general formula R (Ni) _a (Co) _b
(Al) _c (M) _d , where R is 77% by weight or more of L
a and at least 23% by weight of one or more rare earth metals other than La, wherein M is Fe, Cr, C
This was achieved by a hydrogen storage alloy comprising at least one metal selected from the group consisting of u and Mn, wherein a to d are positive ratio molar ratios (R is 1) in the following ranges.
3.0 ≦ a ≦ 4.5; 0.3 ≦ b ≦ 1.0; 0 <c ≦
0.6; 0 <d ≦ 0.5 Further, Ti
Suitable results are obtained when the content of Pb is 0.05% by weight or less and the content of Pb is 0.05% by weight or less. Further, by adding 0.3% by weight or less of oxygen, 0.05% by weight or less of carbon, and 0.05% by weight or less of sulfur, which are nonmetallic elements, to the hydrogen storage alloy in addition to Ti and Pb. It has been found that more favorable results can be obtained.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The La—Ni-based hydrogen storage alloy according to the present invention has a high La content in a rare earth mixture on the La side and a small amount of Mg added thereto to provide a high-temperature low-temperature alloy. The capacity was maintained and the cycle life was improved. Also, by increasing the La content on the La side, the dissociation equilibrium pressure can be adjusted to a range suitable for an alkaline secondary battery, so that the substitution amount of Mn or the like or Al on the Ni side can be made smaller than before. It is suitable for an alloy for a negative electrode of an alkaline secondary battery having a high capacity and a good cycle life.

The La side of the present invention is represented by the general formula R
a may be contained in an amount of 77% by weight or more, and particularly preferably a mixture containing 77 to 95% by weight of La and 5 to 23% by weight of one or more rare earth metals other than La. If the La content in the general formula R is less than 77% by weight, the effect at low temperatures as obtained in the present invention cannot be expected.
If the La content in the general formula R exceeds 95% by weight, the economy tends to deteriorate. In the present invention, La is particularly set to 7
It is preferable to contain 7 to 90% by weight.

The rare earth elements other than La in the general formula R include Ce, Pr, Nd, Sm, Eu, Gd, Tb, D
y, Ho, Er, Tm, Yb, Lu, Y, at least one selected from the group consisting of 23% by weight or less, preferably 5% by weight or less.
Contains 23% by weight. Preferably, one or more of Pr, Ce, and Nd are selected, and the content of R is preferably 5 to 23% by weight. Among them, Ce and P are particularly preferable.
r or Nd may be contained in an amount of 10 to 23% by weight. Further, when R containing one or more members selected from the group consisting of Ce, Pr and Nd and La is used, the ratio of the total to R is 95 to 100% by weight, and the balance (R
(5% by weight) is preferably one or more of the other rare earth elements.

The general formula R (Ni) _a (Co) _b (A
1) In _c (M) _d , the amount of Ni is such that a is in the range of 3.0 to 4.5 moles when R is 1 mole. If the amount of Ni is less than this range, the capacity will decrease, and if it is more than this range, the cycle life will decrease. Hereinafter, b, c,
Also for d, the number of moles when R is 1 mole, that is,
Represents the molar ratio. Further, Co and Al can each improve the corrosion resistance of the hydrogen storage alloy. The content of Co is 0.1.
3 ≦ b ≦ 1.0, and particularly preferably 0.4 ≦ b ≦ 0.7. If it is less than 0.3, the cycle life tends to decrease. If it exceeds 1.0, it is not preferable in terms of low-temperature characteristics and high-rate discharge characteristics. The content c of Al is 0 <c ≦
0.6, but preferably 0.2 ≦ c ≦ 0.5.
If it does not contain Al, the cycle life is reduced, and if it exceeds 0.6, the capacity is undesirably reduced.

M is at least one metal selected from the group consisting of Fe, Mn, Cr and Cu, and particularly preferably Mn and Cr. For example, the addition of Mn has the effect of lowering the dissociation equilibrium pressure of hydrogen and increasing the capacity, and the addition of Cr has the effect of increasing the initial activity and making it difficult to shorten the life even when the La content is high. However, in order to reduce the cycle life, the amount d of M is 0 <d ≦ 0.5,
5 ≦ d ≦ 0.3 is preferred. If M is not included, the capacity is reduced, and if it exceeds 0.5, the cycle life is undesirably reduced. Furthermore, in the present invention, in the Ni-side composition,
The sum of a, b, c, and d (a + b + c + d) is 4.5 to 4.5.
It is advisable to increase the hydrogen storage capacity to 5.5.

Next, the effect of the element contained in a very small amount, which is a feature of the present invention, is that Mg is contained in a large amount of La, and thus, when assembled in an alkaline secondary battery, alkaline electrolysis is performed at an extremely early stage. It dissolves preferentially in a liquid and improves the low-temperature characteristics in the initial stage by increasing the surface area of the surface of the hydrogen storage alloy. The addition amount of Mg is 50 to 500 ppm.
Preferably, more preferably 100 ppm to 400 ppm
It is. If it is less than 50 ppm, the discharge capacity decreases, and furthermore, the effect of low-temperature characteristics cannot be obtained. If it exceeds 500 ppm, the cycle life decreases.

The present invention is characterized in that the above-mentioned trace Mg-containing alloy further contains trace amounts of Ti, Pb, C, O and S. In the present invention, by further adding Ti to the alloy, a Ti-Ni intermetallic compound is produced, which is mainly precipitated at the grain boundaries in the matrix, and the hydrogen storage alloy is expanded and contracted when hydrogen is stored and released. It tends to be a starting point for cracks in the steel, and improves the initial low-temperature characteristics, particularly the discharge characteristics at low temperatures. Also, when a trace amount of oxygen is present, it forms carbides and gives good initial low-temperature properties, as described below. The addition amount of Ti is 0.05% by weight or less, preferably 0.005 to 0.05% by weight, and more preferably 0.01 to 0.04% by weight. If the amount is less than 0.005% by weight, the effect of the present invention may not be obtained in some cases.
If the amount is more than 10% by weight, the cycle life decreases.

Further, Pb has an effect of being eluted in an alkaline electrolyte when assembled into an alkaline secondary battery and increasing the discharge voltage of the battery system, and improves discharge characteristics at low temperatures.
The content of Pb is 0.05% by weight or less, preferably 0.0% by weight.
01-0.05% by weight, preferably 0.005-0.0%
4% by weight. If the amount is less than 0.001% by weight, the effect of the present invention may not be obtained. If the amount is more than 0.05% by weight, the voltage at the time of charging increases, which is not preferable as an alkaline secondary battery.

Further, the oxygen content in the hydrogen storage alloy is 0.3% by weight or less, preferably 0.01 to 0.3% by weight, more preferably 0.03 to 0.2% by weight. If the content is less than 0.01% by weight, the activity may be so strong that handling may be difficult. If the content exceeds 0.3% by weight, the oxide film on the alloy surface may hinder the reaction on the alloy surface when an alkaline secondary battery is used. , Degrades high rate discharge characteristics and the like. Further, the adjustment of the oxygen content in the hydrogen storage alloy can be easily performed by controlling the atmosphere during the manufacturing process.

[0017] The carbon contained in a trace amount preferentially combines with the rare earth metal element and Ti in the hydrogen storage alloy to form a carbide, and mainly precipitates at the grain boundaries in the matrix and absorbs and releases hydrogen. Easy to become the starting point of cracking of the hydrogen storage alloy due to expansion and contraction in the case, initial low temperature characteristics,
Particularly, the high-rate discharge characteristics and the like on the low temperature side required for recent portable devices are improved. The carbon content is 0.05% by weight or less, preferably 0.005 to 0.05% by weight, and more preferably 0.01 to 0.04% by weight. 0.005
If the content is less than 0.05% by weight, the formation of carbides of Ti-C may not occur. If the content is more than 0.05% by weight, the amount of Ti-C precipitated at the grain boundary is too large, and the properties deteriorate.

The sulfur content is 0.05% by weight or less, preferably 0.001 to 0.05% by weight, more preferably 0.0% by weight.
It is a content of 03 to 0.04% by weight. Sulfur easily forms sulfides, especially with Ni and Co in the hydrogen storage alloy. If the content exceeds 0.05% by weight, the formed Ni and Co sulfides are passivated to cause a decrease in high-rate discharge characteristics. , 0.0
If the content is less than 01% by weight, when assembled into an alkaline secondary battery, Ni and Co are eluted in the alkaline electrolyte and the cycle life may be easily reduced due to a decrease in the electrolyte.

The present invention is particularly directed to a method of the present invention wherein the La side contains 77% by weight or more of La and one or more rare earth elements other than La, contains 50 to 500 ppm of Mg, and further contains metals other than rare earths such as Ti and Pb and O , C and S are preferably contained within a predetermined range. Although the present invention is an alloy having the above composition, the effect can be enhanced by adding a metal element other than the above elements.

The hydrogen storage alloy of the present invention is prepared by weighing a predetermined amount of each element, and using a crucible or the like in a high-frequency melting furnace or arc melting furnace under vacuum (under a low pressure of 0.01 Torr or less) or inert gas such as Ar. After melting in a gas atmosphere at 200-800 Torr,
At 300 to 1600 ° C., an ingot is cast into an iron mold or the like. In this case, the La side can be charged with a rare earth element, or can be added to the misch metal to have a predetermined amount. Furthermore, in vacuum (0.01 Torr
Under the following low pressure) or under an inert gas atmosphere such as Ar (600).
~ 1000 Torr) at 800-1200 ° C
Heat treatment is performed for 20 hours. The alloy of the present invention can be obtained by a roll quenching method, a gas atomizing method, or a disk atomizing method in addition to the casting method. The hydrogen storage alloy produced by the above method can be easily obtained by pulverizing it under an inert atmosphere such as Ar, nitrogen or the like by an impact type or grinding type pulverizer so as to have an average particle size of 5 to 50 μm. Further, the alloy powder of the present invention may be subjected to a surface treatment with an alkali solution such as potassium hydroxide or the like, an acidic solution such as hydrochloric acid or the like, or a metal layer may be formed on the alloy surface with a transition metal such as Ni or Co and activated. Good.

The hydrogen-absorbing alloy powder thus obtained is melted using a binder such as polyvinyl alcohol, carboxymethylcellulose, cellulose such as methylcellulose, or a binder such as PTFE, polyethylene oxide or polymer latex to form a paste. An electrode can be easily formed by filling a three-dimensional conductive support such as a nickel fiber body or a two-dimensional conductive support such as punched metal. The binder is preferably used in an amount of 0.1 to 20 parts by weight based on 100 parts by weight of the alloy. Further, if necessary, carbon graphite, N
0.5 to 10 parts by weight of a conductive aid such as i powder may be added. The alkaline storage battery using the hydrogen storage alloy of the present invention as a negative electrode has a high capacity, a long cycle life when charging and discharging are repeated, and has excellent high rate discharge characteristics and low temperature discharge characteristics. The alloy of the present invention can be used as a storage means such as a heat pump as an application other than the electrode.

[0022]

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. Examples 1 to 30, Comparative Examples 1 to 8 La (purity 99% by weight or more), Ce (purity 99% by weight or more), Pr (purity 99% by weight or more), Nd (purity 99% by weight or more), Ni (purity) 99% by weight or more), Co (99% by weight or more), Mn (99% by weight or more), Al
(Purity 99% by weight or more), Cr (Purity 99% by weight or more)
Were weighed and mixed to obtain the composition shown in Tables 1 and 2. In Tables 1 and 2, the sum of the La side, that is, the R side (La, Ca, Pr, Nd) is 1.0.
, The Ni side (Ni, Co, Al, Mn, C
r) was added in a molar ratio such that the total sum was 5.0. In addition, the columns of “additional elements” in Tables 1 and 2 represent ppm or% by weight based on the entire alloy. Further, other additional elements such as Mg are added, heated and melted (1400 ° C.) by high frequency melting under argon, and further heat-treated at 760 Torr and 900 ° C. for 5 hours in an Ar atmosphere to have compositions shown in Tables 1 and 2. A hydrogen storage alloy was manufactured. The obtained alloy was pulverized and pulverized so as to have an average particle diameter of 35 μm to obtain a hydrogen storage alloy powder. Regarding the oxygen amount, a hydrogen storage alloy having a predetermined oxygen amount was obtained by adjusting the oxygen concentration in the inert gas (Ar) in each unit operation of high frequency melting, heat treatment, and pulverization.

An aqueous solution of 3% by weight of polyvinyl alcohol (average degree of polymerization: 2,000, saponification degree: 98 mol%) is mixed with 2.5 g of a 10 wt% powder to form a paste. 30 in porous body
After filling and drying by vol.
A 1.0 mm electrode plate was manufactured, and then a lead wire was attached to obtain a negative electrode. Using a sintered electrode for the positive electrode, and bonding it to the negative electrode via a polypropylene separator, 6NK
The battery was fabricated by immersion in an OH electrolyte.

The obtained battery was charged to the negative electrode capacity at 20 ° C. at 120% at 0.1 C, and after a 1-hour pause, discharged at 0.2 C until the battery voltage reached 0.6 V (the above was 1 to 1). Cycle). After repeating this cycle five times, the high-rate discharge characteristics and the low-temperature discharge characteristics (−10
C and -18 ° C). Also,
The cycle life is the ratio of the capacity at 200 cycles to the capacity at 5 cycles after repeating this cycle 200 times. Table 3 shows the results. In Comparative Examples 1 to 8, a battery test was performed after producing an alloy in the same manner as in Example. The results are shown in Tables 3 and 4.

[0025]

The hydrogen storage alloy of the present invention has a high capacity and a long cycle life, and has a high rate discharge characteristic and an excellent discharge characteristic at a low temperature due to the effect of a small amount of added elements such as Mg. It is suitable as.

[0026]

[Table 1]

[0027]

[Table 2]

[0028]

[Table 3]

[0029]

[Table 4]

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Satoshi Shima 2-5-1-5 Kitafu, Takefu-shi, Fukui Shin-Etsu Kagaku Kogyo Co., Ltd. Magnetic Materials Research Laboratory (72) Inventor Takao Maeda 2-1-1 Kitafu, Takefu-shi, Fukui No. 5 Shin-Etsu Kagaku Kogyo Co., Ltd. Magnetic Materials Research Laboratory

Claims (3)

[Claims] 1. The general formula R (Ni) _a (Co) _b (Al)
_c (M) _d (wherein R is at least 77% by weight of La and 23
Represents a mixture having up to 1% by weight of one or more rare earth metals other than La. M represents one or more metals selected from the group consisting of Fe, Cr, Cu, and Mn. ad are
A positive number representing the molar ratio to R, and 3.0 ≦ a ≦
4.5; 0.3 ≦ b ≦ 1.0; 0 <c ≦ 0.6; 0 <d
≦ 0.5. ), 50 to 500 ppm of M
Hydrogen storage alloy containing g. 2. The hydrogen storage alloy according to claim 1, further comprising 0.05% by weight or less of Ti and 0.05% by weight or less of Pb in the alloy. 3. The hydrogen storage according to claim 2, further comprising 0.3% by weight or less of oxygen, 0.05% by weight or less of carbon, and 0.05% by weight or less of sulfur in the alloy. alloy.