JP2000265229A - Hydrogen storage alloy and secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the flatness characteristic of equilibrium pressure at the occlusion and release of hydrogen and also to reduce pressure difference by providing a specific composition consisting of Mg, La, two or more kinds among rare earth elements including Y, Ni, Co, and one or more elements selected from among Mn and other twelve elements. SOLUTION: The hydrogen storage alloy has a composition represented by general formula Mg(La1-bR1b)1-aNiXCoYM1Z [where R1 means two or more elements selected from rare earth elements including Y and Ce content based on the total content of R1 and La is regulated to <20 wt.%; M1 means one or more elements selected from Mn, Fe, V, Cr, Nb, Al, Ga, Zn, Sn, Cu, Si, P, and B; and 0.15<a<0.35, 0.55<=b<=0.95, 0<=Y<=1.5, 0<=Z<=0.2 and 2.9<X+Y+Z<3.5 are satisfied]. Because the secondary battery having a cathode containing this alloy can maintain high working voltage over a long period at electric discharge, discharge capacitance and charge-and-discharge cycle life can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a hydrogen storage alloy and a secondary battery.

[0002]

2. Description of the Related Art A hydrogen storage alloy is an alloy that can safely and easily store hydrogen as an energy source, and is attracting much attention as a new energy conversion and storage material. The fields of application of hydrogen storage alloys as functional materials are:
Hydrogen storage / transport, heat storage / transport, thermo-mechanical energy conversion, hydrogen separation / purification, hydrogen isotope separation, batteries using hydrogen as active material, catalysts in synthetic chemistry, temperature sensors, etc. Have been proposed throughout. In particular, application and practical application to metal oxide / hydrogen secondary batteries are being actively pursued, and research and development for higher capacity and longer life are being pursued.

Meanwhile, AB ₅ type rare earth as the hydrogen storage alloy - a nickel-based intermetallic compounds have been put to practical use. The rare earth-nickel intermetallic compound is AB ₅
There are many other than types. Mat. Res. Bull
l. , 11, (1976) in 1241, it is disclosed that an intermetallic compound containing large amounts than the rare earth element AB ₅ type is absorbing a large amount of hydrogen at about room temperature than ₅ type AB. Further, in an example in which the A site is a mixture of a rare earth element and Mg, J. Less-Common Metals,
73, have been reported La _1-X Mg X Ni ₂ type alloy (1980) 339. However, both have problems in that the stability with hydrogen is too high to release hydrogen, and that depending on the composition, alloy components are separated into stable hydrides and metals with hydrogenation.

On the other hand, if the rare earth-Mg—Ni-based hydrogen storage alloy contains an appropriate amount of Mg and the Ce content in the rare earth component is within a controlled range, the rare earth-Mg—Ni hydrogen storage alloy has a regular structure, and is difficult to store and release hydrogen. It is known that there is almost no separation of the alloy components involved.

However, in such a hydrogen storage alloy, the difference between the equilibrium pressure at the time of hydrogen storage and the equilibrium pressure at the time of hydrogen release becomes large especially in a region where the ratio of the number of hydrogen atoms to the number of metal atoms is small, and the hydrogen gas storage When completely recovering hydrogen by using it as a tool, there is a problem that the pressure is considerably lower than the pressure applied at the time of occlusion.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a hydrogen storage alloy having high flatness of equilibrium pressure at the time of hydrogen storage and release and a reduced pressure difference at the time of hydrogen storage and release. Aim.

Another object of the present invention is to provide a hydrogen storage alloy having an improved hydrogen storage / release rate.

Another object of the present invention is to provide a secondary battery having improved discharge capacity and cycle life.

Another object of the present invention is to provide a secondary battery in which the hydrogen storage alloy is prevented from being corroded and oxidized by an alkaline electrolyte, and the high-rate discharge characteristics are improved.

An object of the present invention is to provide a secondary battery in which the hydrogen storage alloy is prevented from being corroded and oxidized by an alkaline electrolyte, and the discharge capacity and the charge / discharge cycle life are improved.

[0011]

According to the present invention, there is provided a hydrogen storage alloy having a composition represented by the following general formula (1).

Mg _a (La _1−b R1 _b ) _1−a Ni _X Co _Y M1 _Z (1) where R1 is at least two kinds of elements selected from rare earth elements containing Y, and The Ce content is less than 20% by weight based on the total amount of La, and M1 is M
n, Fe, V, Cr, Nb, Al, Ga, Zn, Sn,
At least one element selected from Cu, Si, P and B, and the atomic ratios a, b, X, Y and Z are each 0.15.
<A <0.35, 0.55 ≦ b ≦ 0.95, 0 ≦ Y ≦
1.5, 0 ≦ Z ≦ 0.2, 2.9 <X + Y + Z <3.5
Is defined as

According to the present invention, a positive electrode, a negative electrode containing a hydrogen storage alloy having a composition represented by the following general formula (1), a separator interposed between the positive electrode and the negative electrode, And a secondary battery.

Mg _a (La _1−b R1 _b ) _1−a Ni _X Co _Y M1 _Z (1) where R1 is at least two kinds of elements selected from rare earth elements including Y, and The Ce content is less than 20% by weight based on the total amount of La, and M1 is M
n, Fe, V, Cr, Nb, Al, Ga, Zn, Sn,
At least one element selected from Cu, Si, P and B, and the atomic ratios a, b, X, Y and Z are each 0.15.
<A <0.35, 0.55 ≦ b ≦ 0.95, 0 ≦ Y ≦
1.5, 0 ≦ Z ≦ 0.2, 2.9 <X + Y + Z <3.5
Is defined as

According to the present invention, there is provided a hydrogen storage alloy having a composition represented by the following general formula (2).

Mg _a R 2 _1-ab T1 _b Ni _ZXY Al _X M2 _Y (2) wherein R2 is at least one element selected from rare earth elements containing Y and the La content is less than 55% by weight. And T1 is Ca, Ti, Zr, Hf, Li, Na,
At least one element selected from the group consisting of K, Rb, Cs, Sr and Ba, and M2 is Co, Mn, Fe, Ga, Zn,
Sn, Cu, Si, B, Nb, W, Mo, V, Cr, T
a, P, and at least one element selected from S and the atomic ratios a, b, X, Y, and Z are each 0.1 ≦ a <0.
3, 0 ≦ b ≦ 0.3, 0.2 <X <0.7, 0.1 ≦ Y
≦ 3.0, 3.25 ≦ Z ≦ 4.5.

According to the present invention, a positive electrode, a negative electrode containing a hydrogen storage alloy having a composition represented by the following general formula (2), a separator interposed between the positive electrode and the negative electrode, And a secondary battery.

Mg _a R 2 _1-ab T1 _b Ni _ZXY Al _X M2 _Y (2) where R2 is at least one element selected from rare earth elements containing Y and the La content is less than 55% by weight. And T1 is Ca, Ti, Zr, Hf, Li, Na,
At least one element selected from the group consisting of K, Rb, Cs, Sr and Ba, and M2 is Co, Mn, Fe, Ga, Zn,
Sn, Cu, Si, B, Nb, W, Mo, V, Cr, T
a, P, and at least one element selected from S and the atomic ratios a, b, X, Y, and Z are each 0.1 ≦ a <0.
3, 0 ≦ b ≦ 0.3, 0.2 <X <0.7, 0.1 ≦ Y
≦ 3.0, 3.25 ≦ Z ≦ 4.5.

According to the present invention, it has a composition represented by the following general formula (3), and has a M
A hydrogen storage alloy is provided, wherein a region where the g concentration is 0.5 to 2 times the average value is present in 70% or more.

Mg _a R 3 _1-ab T 2 _b Ni _Zx M 3 _x (3) wherein R 3 is at least one element selected from rare earth elements including Y, and T 2 is Ca, Ti, Zr and Hf
At least one element selected from the group consisting of Co, M
n, Fe, Al, Ga, Zn, Sn, Cu, Si, B,
At least one element selected from Nb, W, Mo, V, Cr, Ta, Li, P and S, and the atomic ratios a, b, X and Z are respectively 0.2 ≦ a ≦ 0.35 and 0 ≦ b. ≦ 0.
3, 0 <X ≦ 2.0, 3 ≦ Z ≦ 3.8.

According to the present invention, the positive electrode and a region having a composition represented by the following general formula (3) and having a Mg concentration per unit area of 0.5 to 2 times the average in the cross section are defined. A secondary battery is provided, comprising: a negative electrode containing a hydrogen storage alloy present at 70% or more, a separator interposed between the positive electrode and the negative electrode, and an alkaline electrolyte.

Mg _a R 3 _1-ab T 2 _b Ni _ZX M 3 _X (3) where R 3 is at least one element selected from rare earth elements including Y, and T 2 is Ca, Ti, Zr and Hf
At least one element selected from the group consisting of Co, M
n, Fe, Al, Ga, Zn, Sn, Cu, Si, B,
At least one element selected from Nb, W, Mo, V, Cr, Ta, Li, P and S, and the atomic ratios a, b, X and Z are respectively 0.2 ≦ a ≦ 0.35 and 0 ≦ b. ≦ 0.
3, 0 <X ≦ 2.0, 3 ≦ Z ≦ 3.8.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, first to third hydrogen storage alloys according to the present invention will be described.

(First Hydrogen Storage Alloy) This hydrogen storage alloy has a composition represented by the following general formula (1).

Mg _a (La _{1 -b} R _{1 b} ) _{1 -a} Ni _X Co _Y M 1 _Z (1) where R 1 is at least two kinds of elements selected from rare earth elements containing Y, and The Ce content is less than 20% by weight based on the total amount of La, and M1 is M
n, Fe, V, Cr, Nb, Al, Ga, Zn, Sn,
At least one element selected from Cu, Si, P and B, and the atomic ratios a, b, X, Y and Z are each 0.15.
<A <0.35, 0.55 ≦ b ≦ 0.95, 0 ≦ Y ≦
1.5, 0 ≦ Z ≦ 0.2, 2.9 <X + Y + Z <3.5
Is defined as

When the atomic ratio a is out of the above range, the hydrogen release characteristics and the cycle characteristics deteriorate. A more preferable range of the atomic ratio a is 0.2 ≦ a ≦ 0.3.

R1 is preferably composed of three or more kinds of rare earth elements. As such R1, for example,
Misch metal, which is a mixture of rare earth elements, can be mentioned. R1 is preferably composed of three or more kinds of rare earth elements selected from Pr, Nd, Sm and Y. R1 has a Ce content of less than 20% by weight based on the total amount of R1 and La, or does not contain Ce. The Ce content is 20 with respect to the total amount of R1 and La.
When the content is not less than% by weight, the phase having the CaCu ₅ type crystal structure increases, and the equilibrium pressure at the end of the release of gaseous hydrogen may be significantly reduced. More preferably, the Ce content is 15% by weight or less.

By setting the atomic ratio b of R1 in the above range, the problem of difficulty in releasing hydrogen can be improved, and a hydrogen storage alloy having a large hydrogen storage amount can be obtained. If the atomic ratio b is less than 0.55, the number of occlusion sites at which hydrogen becomes too stable increases, and the hydrogen equilibrium pressure required for complete release is reduced. On the other hand, the atomic ratio b
Exceeds 0.95, it is necessary to increase the heat treatment temperature when performing heat treatment to improve the homogeneity of the hydrogen storage alloy, the amount of Mg evaporated during the heat treatment increases, and it is extremely difficult to control the composition. Might be. A more preferable range of the atomic ratio b is 0.6 ≦ b ≦ 0.8.

By incorporating Co into the hydrogen storage alloy, the flatness of the storage equilibrium pressure during storage can be improved. If the atomic ratio Y exceeds 1.5, the amount of occlusion decreases significantly. A more preferable range of the atomic ratio Y is 0.
5 ≦ Y ≦ 1.0.

By including the element M1 in the hydrogen storage alloy, the hydrogen storage / release characteristics such as the hydrogen storage / release speed can be improved, and the equilibrium hydrogen pressure can be adjusted to an appropriate range. This is presumed to be due to the diffusion of hydrogen that has entered the alloy due to the element M1, and the easy storage and release of the hydrogen storage alloy.
More preferably, Mn, Al, Si, Cr and Fe are used as the element M1. The atomic ratio Y of the element M1 is 0.2
If it exceeds, the amount of hydrogen storage / release will decrease. A more preferable range of the atomic ratio Y is 0.01 ≦ Y ≦ 1.5, and a still more preferable range is 0.05 ≦ Y ≦ 1.0.

The sum of the atomic ratios X, Y and Z is defined in the above range for the following reason. When the total value of the atomic ratios X, Y, and Z is 2.9 or less, the number of sites in the alloy where hydrogen is stabilized is significantly increased, so that the equilibrium pressure at the end of the release of gaseous hydrogen in the alloy is significantly reduced. . By making this sum greater than 2.9,
Hydrogen storage / release characteristics can be improved.
However, if the total value of the atomic ratios X, Y, and Z is set to 3.5 or more, it becomes difficult to homogenize by heat treatment, and a different phase may be generated to impair the flatness of the equilibrium pressure at the time of absorbing and releasing hydrogen. A more preferable range of the total value is 3.0 <X
+ Y + Z <3.4.

Further, the first hydrogen storage alloy according to the present invention allows elements such as C, N, O and F as impurities to be contained within a range that does not impair the characteristics. The content of each of these impurities is preferably 1% by weight or less.

This hydrogen storage alloy is produced, for example, by the methods described in the following (1) to (3).

(1) Each of the elements is weighed, and the alloy is prepared in an inert atmosphere such as argon gas by a molten metal quenching method such as a single roll method or a twin roll method, or a super quenching method such as a gas atomizing method. I do.

(2) Each element is weighed, high-frequency induction-melted in an inert atmosphere such as argon gas, and cast into a mold or the like to produce the alloy.

(3) RNi ₅ system, R ₂ Ni ₇ system, RNi
₃ series, RNi ₂ series, Mg ₂ Ni series, MgNi ₂ series etc. mother alloy is produced by high frequency induction melting, each mother alloy is weighed to obtain the target composition, and this is high frequency induction melted to mold. The above alloy is produced by casting to the above.

The first hydrogen storage alloy according to the present invention is preferably subjected to a heat treatment in a vacuum or in an inert atmosphere at a temperature of 300 ° C. or more and less than the melting point. Such heat treatment can reduce the abundance of the AB ₅ phase and the AB ₂ phase in the alloy and can reduce lattice distortion, thereby improving hydrogen storage / release characteristics such as hydrogen storage / release speed. Can be. A more preferable range of the heat treatment temperature is 750 ° C to 1050 ° C. A more preferred range is from 800 to 1000C. Further, the optimal heat treatment time varies depending on the heat treatment temperature, but as a guide, it is 0.1 to 500 hours, preferably 0.5 to 500 hours.
-100 hours, more preferably 1-20 hours.

(Second Hydrogen Storage Alloy) This hydrogen storage alloy has a composition represented by the following general formula (2).

Mg _a R 2 _1-ab T1 _b Ni _ZXY Al _X M2 _Y (2) where R2 is at least one element selected from rare earth elements containing Y and the La content is less than 55% by weight. And T1 is Ca, Ti, Zr, Hf, Li, Na,
At least one element selected from the group consisting of K, Rb, Cs, Sr and Ba, and M2 is Co, Mn, Fe, Ga, Zn,
Sn, Cu, Si, B, Nb, W, Mo, V, Cr, T
a, P, and at least one element selected from S and the atomic ratios a, b, X, Y, and Z are each 0.1 ≦ a <0.
3, 0 ≦ b ≦ 0.3, 0.2 <X <0.7, 0.1 ≦ Y
≦ 3.0, 3.25 ≦ Z ≦ 4.5.

When the atomic ratio a of Mg is out of the above range, the hydrogen release characteristics and the cycle characteristics of the hydrogen storage alloy deteriorate,
Further, it becomes difficult to realize a secondary battery having a large discharge capacity and excellent cycle characteristics. A more preferable range of the atomic ratio a is 0.15 ≦ a ≦ 0.28.

As R2, it is preferable to use at least one element selected from La, Ce, Pr, Nd and Y in consideration of cost reduction of the hydrogen storage alloy electrode. Among them, it is more preferable to use misch metal which is a mixture of rare earth elements.

If the La content in R2 exceeds 55% by weight when the Al atomic ratio X is in the above-mentioned range, the hydrogen storage / release rate of the alloy is reduced, and the cycle life of the secondary battery is shortened. Therefore, the effect of including a specific amount of Al cannot be obtained. The La content is more preferably set to 50% by weight or less. On the other hand, if the La content is less than 1.0% by weight, the equilibrium pressure during occlusion becomes too high.
It becomes difficult to occlude. Therefore, the lower limit of the La content is preferably set to 1.0% by weight.

R2 has a Ce content of less than 20% by weight (0%).
% By weight). Atomic ratio X of Al
When Ce content upon the range described above and exceeds 20 wt%, AB ₅ type for phase having a crystal structure may become large, high-rate discharge of the hydrogen absorption and desorption rates and a secondary battery of the alloy There is a possibility that the characteristics and cycle life cannot be improved.

When the hydrogen storage alloy is subjected to heat treatment, the temperature of the heat treatment can be lowered by adding T1 to the alloy, so that the homogeneity of the alloy can be improved. As T1, Ti, Zr, Li, Sr, B
It is preferable to use a. Further, when the atomic ratio b of T1 exceeds 0.3, the heat treatment temperature is greatly reduced,
The main phase of the alloy is decomposed, and the discharge capacity of the secondary battery decreases. A more preferable range of the atomic ratio b is 0.05 ≦ b ≦
0.2.

When the atomic ratio X of Al is out of the above range, the hydrogen absorbing / desorbing speed of the hydrogen storage alloy, the corrosion resistance to an alkaline aqueous solution such as an alkaline electrolyte, and the high-rate discharge characteristics and cycle life of the secondary battery are improved. It becomes difficult to make it. A more preferable range of the atomic ratio X is 0.25 ≦ X
≦ 0.6.

By including the element M2 in the hydrogen storage alloy, the hydrogen storage / release characteristics such as the hydrogen storage / release speed of the alloy can be improved, and the cycle characteristics of the secondary battery can be dramatically improved. be able to. It is presumed that the improvement in the hydrogen storage / release characteristics is due to the diffusion of hydrogen that has entered the alloy due to the element M2 and the easy storage / release of the hydrogen storage alloy. As M2, Co, Mn, Fe, Ga, Cu,
It is preferable to use Si and Cr. When the atomic ratio Y of the element M2 is out of the above range, high hydrogen storage /
No release rate is obtained, and the discharge capacity of the secondary battery is reduced. A more preferable range of the atomic ratio Y is 0.05 ≦ Y ≦ 1.
0, and a more preferable range is 0.1 ≦ Y ≦ 0.8.

When the atomic ratio Z is out of the above range, the hydrogen release characteristics and the cycle characteristics of the hydrogen storage alloy deteriorate, and it is difficult to realize a secondary battery having a large discharge capacity and excellent cycle characteristics. Become. A more preferable range of the atomic ratio Z is 3.3 ≦ Z ≦ 4.0.

Further, the second hydrogen storage alloy according to the present invention allows elements such as C, N, O, and F to be contained as impurities within a range that does not impair the characteristics. The content of each of these impurities is preferably 1% by weight or less.

This hydrogen storage alloy is produced by the same method as described for the first hydrogen storage alloy.

The second hydrogen storage alloy according to the present invention can be used at a temperature of 300 ° C. or more in a vacuum or in an inert atmosphere.
It is preferable that the heat treatment is performed at a temperature lower than 00 ° C. Such heat treatment can reduce the abundance of the AB ₅ phase and the AB ₂ phase in the alloy, so that the hydrogen storage / release characteristics such as the hydrogen storage / release speed of the hydrogen storage alloy can be further improved, The high rate discharge characteristics and cycle life of the secondary battery can be further improved. On the other hand, if the heat treatment temperature exceeds 1200 ° C., the main phase of the alloy may be decomposed and a high hydrogen storage / release rate may not be obtained. A more preferable range of the heat treatment temperature is 400 ° C to 10 ° C.
00 ° C. Further, the optimal heat treatment time varies depending on the heat treatment temperature, but it is 5 to 100 as a guide.
0 hour, preferably 10 to 800 hours, more preferably 50 to 600 hours.

(Third Hydrogen Storage Alloy) This third hydrogen storage alloy has a composition represented by the following general formula (3), and the Mg concentration per unit area in the cross section is an average per unit area. The region corresponding to 0.5 to 2 times the Mg concentration is 7
0% or more.

Mg _a R 3 _1-ab T 2 _b Ni _ZX M 3 _X (3) where R 3 is at least one element selected from rare earth elements including Y, and T 2 is Ca, Ti, Zr and Hf
At least one element selected from the group consisting of Co, M
n, Fe, Al, Ga, Zn, Sn, Cu, Si, B,
At least one element selected from Nb, W, Mo, V, Cr, Ta, Li, P and S, and the atomic ratios a, b, X and Z are respectively 0.2 ≦ a ≦ 0.35 and 0 ≦ b. ≦ 0.
3, 0 <X ≦ 2.0, 3 ≦ Z ≦ 3.8.

When the atomic ratio a of Mg is out of the above range, the hydrogen release characteristics and cycle characteristics of the hydrogen storage alloy deteriorate,
Further, it becomes difficult to realize a secondary battery having a large discharge capacity and excellent cycle characteristics. A more preferable range of the atomic ratio a is 0.25 ≦ a ≦ 0.32.

As R3, it is preferable to use at least one element selected from La, Ce, Pr, Nd and Y in consideration of cost reduction of the hydrogen storage alloy electrode. Among them, it is more preferable to use misch metal which is a mixture of rare earth elements. Examples of such a misch metal include Mm rich in Ce and Lm rich in La.

R3 has a Ce content of less than 20% by weight (0%).
% By weight). Ce content is 2
If the content exceeds 0% by weight, a phase having an AB ₅ type crystal structure is likely to be generated, so that the amount of the region where the Mg concentration is restricted in the cross section may be smaller than 70%.

By including the element T2, the characteristics such as the hydrogen release rate can be improved without significantly reducing the hydrogen storage amount of the hydrogen storage alloy, and the alloy is prevented from being finely divided due to hydrogen storage and release. can do.
When the atomic ratio b of T2 exceeds 0.3, the effects described above, that is, the improvement of the hydrogen release characteristics and the suppression of the pulverization cannot be seen, and the discharge capacity of the secondary battery decreases. The smaller the atomic ratio b, the longer the cycle life of the secondary battery tends to be. From the viewpoint of ensuring a long life, the upper limit of the atomic ratio b of T is preferably set to 0.2.

By including the element M3 in the hydrogen storage alloy, the hydrogen storage / release characteristics such as the hydrogen storage / release speed of the alloy can be improved, and the cycle characteristics of the secondary battery can be dramatically improved. be able to. It is presumed that the improvement in the hydrogen storage / release characteristics is caused by the diffusion of hydrogen that has entered the alloy due to the element M3 and the easy storage / release of the hydrogen storage alloy. As the element M3, Co, Mn, Fe, Al, G
More preferably, a, Cu, Si, Cr, and Li are used. When the atomic ratio X of the element M3 exceeds 2.0, the discharge capacity of the secondary battery decreases. A more preferable range of the atomic ratio X is 0.01 ≦ X ≦ 1.5, and a more preferable range is 0.1 ≦ X ≦ 1.5.
05 ≦ X ≦ 1.0.

If the atomic ratio Z is out of the above range, the hydrogen release characteristics and the cycle characteristics of the hydrogen storage alloy deteriorate, and it is difficult to realize a secondary battery having a large discharge capacity and excellent cycle characteristics. Become. A more preferable range of the atomic ratio Z is 3.2 ≦ Z ≦ 3.7.

When the hydrogen storage alloy is in a lump (for example, an ingot or a flake), the Mg concentration per unit area in the cross section of the hydrogen storage alloy is determined by an electron beam microanalyzer (EPMA) at a magnification of 50 to 10,000 times. It can be obtained by taking an electronic image or a reflected electron image and mapping Mg. M per unit area obtained
The average Mg concentration per unit area is calculated from the g concentration, the actual concentration and the average value are compared for each unit area, and the Mg concentration per unit area is 0.5 to 2.0 times the average value. Measure the amount. When the hydrogen storage alloy is in powder form, the Mg concentration per unit area in the cross section of at least five powders is measured by the method described above,
The average Mg concentration per unit area is calculated by adding the Mg concentration distribution in each cross section. The Mg concentration per unit area and the average value are compared for each section, and the M
The area amount where the g concentration is 0.5 to 2.0 times the average value is measured. The average value calculated from the area amount for each section is defined as the area amount required for the hydrogen storage alloy powder.

In the cross section of the hydrogen storage alloy, the Mg concentration per unit area is 0.1% of the average Mg concentration per unit area.
When the area corresponding to 5-2 times becomes less than 70%, M
Since the segregation of g increases, the hydrogen storage / release rate decreases, and the cycle life of the secondary battery decreases. When the segregation of Mg is large, the cycle life of the secondary battery is reduced.
It is presumed that this is because there is a region in the hydrogen storage alloy where corrosion oxidation easily proceeds with respect to the alkaline electrolyte. Further, the region is preferably 85% or more, and most preferably, the region in which the Mg concentration per unit area in the cross section is 0.7 to 1.5 times the average Mg concentration per unit area is 85% or more. There is something.

Further, the third hydrogen storage alloy according to the present invention allows elements such as C, N, O, and F to be contained as impurities within a range that does not impair the characteristics. The content of each of these impurities is preferably 1% by weight or less.

This hydrogen storage alloy is manufactured by the same method as described for the first hydrogen storage alloy.

The third hydrogen storage alloy according to the present invention is preferably subjected to a heat treatment in a vacuum or in an inert atmosphere at a temperature of 750 ° C. or higher and lower than its melting point. Such heat treatment can reduce the abundance of the AB ₅ phase, AB ₂ phase, etc. in the alloy, make the Mg concentration uniform, and alleviate the lattice distortion. Hydrogen storage / release characteristics and the discharge capacity and cycle life of the secondary battery can be further improved. A more preferable range of the heat treatment temperature is 800 ° C.
１1100 ° C. Further, the optimal heat treatment time varies depending on the heat treatment temperature, but as a guideline, it should be set at 0.1 mm.
1 to 500 hours, preferably 0.5 to 100 hours, more preferably 1 to 20 hours.

It is considered that the phase having the target crystal structure of the third hydrogen storage alloy according to the present invention is formed by a peritectic reaction. For this reason, when performing the heat treatment, it is preferable to perform slow cooling at a rate of 20 ° C./min or less in a vacuum or in an inert atmosphere in a temperature region where a peritectic reaction occurs. By performing such slow cooling, the Mg concentration distribution can be made more uniform. Specifically, after holding at 950 ° C. for 30 minutes, it is gradually cooled to 800 ° C. at a rate of 1 ° C./min, and held at 800 ° C. for 30 minutes.
Thereafter, a method of furnace cooling or air cooling can be employed.

Hereinafter, a metal oxide / hydrogen secondary battery (for example, a cylindrical metal oxide / hydrogen secondary battery) as an example of the secondary battery according to the present invention will be described with reference to FIG.

As shown in FIG. 1, an electrode group 5 formed by laminating a positive electrode 2, a separator 3, and a negative electrode 4 and winding them in a spiral shape is accommodated in a cylindrical container 1 having a bottom. ing. The negative electrode 4 is arranged at the outermost periphery of the electrode group 5 and is in electrical contact with the container 1. The alkaline electrolyte is contained in the container 1. Hole 6 in the center
The first sealing plate 7 having a circular shape is disposed at the upper opening of the container 1. Ring-shaped insulating gasket 8
Is disposed between the peripheral edge of the sealing plate 7 and the inner surface of the upper opening of the container 1. And airtightly fixed. One end of the positive electrode lead 9 is connected to the positive electrode 2, and the other end is connected to the lower surface of the sealing plate 7. The positive electrode terminal 10 having a hat shape is attached on the sealing plate 7 so as to cover the hole 6.
The safety valve 11 made of rubber includes the sealing plate 7 and the positive electrode terminal 1.
It is arranged so as to close the hole 6 in a space surrounded by 0. A circular holding plate 12 made of an insulating material having a hole in the center is arranged on the positive electrode terminal 10 such that a protrusion of the positive electrode terminal 10 projects from the hole of the holding plate 12. The outer tube 13 covers the periphery of the holding plate 12, the side surface of the container 1, and the periphery of the bottom of the container 1.

Next, the positive electrode 2, the negative electrode 4, the separator 3
And the alkaline electrolyte will be described.

1) Positive Electrode 2 As long as the positive electrode 2 can be stably charged and discharged in an electrolytic solution, for example, a positive electrode containing nickel hydroxide powder as an active material can be used.

The positive electrode 2 is prepared, for example, by adding a conductive material to nickel hydroxide powder as an active material, kneading it with a binder and water to prepare a paste, filling the paste into a conductive substrate, and drying the paste. After that, it is produced by molding.

The nickel hydroxide powder preferably contains a mixture of nickel hydroxide and at least one metal oxide or hydroxide selected from the group consisting of zinc and cobalt. A nickel-metal hydride secondary battery including such a positive electrode including nickel hydroxide powder and a negative electrode including the hydrogen storage alloy according to the present invention can significantly improve charge / discharge capacity and low-temperature discharge characteristics.

Examples of the conductive material include cobalt oxide, cobalt hydroxide, metallic cobalt, metallic nickel, and carbon.

Examples of the binder include carboxymethylcellulose, methylcellulose, sodium polyacrylate, polytetrafluoroethylene, and polyvinyl alcohol (PVA).

Examples of the conductive substrate include a mesh-like, sponge-like, fiber-like, or felt-like porous metal body made of nickel, stainless steel, or nickel-plated metal.

2) Negative Electrode 4 The negative electrode 4 contains powder of at least one alloy selected from the above-described first to third hydrogen storage alloys.

For pulverizing the hydrogen storage alloy, a method using a pulverizer such as a hammer mill or pin pill in an inert atmosphere can be employed. The average particle size of the hydrogen storage alloy powder is preferably set to 10 to 50 μm.

The negative electrode may be, for example, the following (1):
It is produced by the method described in (2).

(1) A conductive material is added to the above-mentioned hydrogen storage alloy powder, kneaded with a binder and water to prepare a paste, the paste is filled in a conductive substrate, dried, and then molded. Thereby, the negative electrode is manufactured.

(2) A conductive material is added to the powder of the above-mentioned hydrogen storage alloy, kneaded with a binder to prepare a mixture, the mixture is held on a conductive substrate, dried, and then molded. Thereby, the negative electrode is manufactured.

Examples of the binder include those similar to those used for the positive electrode 2. In the case where the negative electrode is manufactured by the method (2) described above, one containing polytetrafluoroethylene (PTFE) is preferable.

Examples of the conductive material include carbon black.

Examples of the conductive substrate include a two-dimensional substrate such as a punched metal, an expanded metal, and a nickel net, and a three-dimensional substrate such as a felt-like metal porous body and a sponge-like metal substrate. it can.

3) Separator 3 The separator 3 is made of, for example, a polymer non-woven fabric such as a polypropylene non-woven fabric, a nylon non-woven fabric, or a non-woven fabric obtained by mixing polypropylene fibers and nylon fibers. In particular, a polypropylene nonwoven fabric whose surface has been hydrophilized is suitable as a separator.

4) Alkaline Electrolyte Examples of the alkaline electrolyte include an aqueous solution of sodium hydroxide (NaOH), lithium hydroxide (LiOH)
Aqueous solution, potassium hydroxide (KOH) aqueous solution, NaO
H and LiOH mixed solution, KOH and LiOH mixed solution, K
A mixed solution of OH, LiOH, and NaOH can be used.

Since the first hydrogen storage alloy according to the present invention described above has the composition represented by the above-described formula (1), the flatness of the equilibrium pressure at the time of storing and releasing hydrogen can be improved. At the same time, the pressure difference at the time of storing and releasing hydrogen can be reduced. A secondary battery provided with a negative electrode containing such a hydrogen storage alloy can maintain a high operating voltage for a long time at the time of discharging, so that the discharge capacity and the charge / discharge cycle life can be improved.

Since the second hydrogen storage alloy according to the present invention has the composition represented by the above-mentioned formula (2), it is possible to suppress corrosion and oxidation caused by an alkaline aqueous solution and to improve the hydrogen storage / release speed. can do. A secondary battery provided with a negative electrode containing such a hydrogen storage alloy can improve the discharge capacity when discharged at a high rate (large current) and can improve the charge / discharge cycle life.

The third hydrogen storage alloy according to the present invention has a composition represented by the above formula (3), and the Mg concentration per unit area in the cross section is an average Mg per unit area.
Since the region corresponding to 0.5 to 2 times the concentration is 70% or more, the hydrogen storage / release characteristics such as the hydrogen storage / release speed can be improved. In addition, a secondary battery including a negative electrode containing the alloy can improve discharge capacity and charge / discharge cycle life. Although the function of the present invention is not clear, it is presumed to be due to the mechanism described below.

That is, the hydrogen storage alloy having the composition represented by the above formula (3) has at least a CaCu ₅ type crystal phase or a MgCu ₂ type crystal phase in addition to the phase having the desired crystal structure. Exists. Thus C
aCu ₅ type crystal phase and MgCu ₂ type crystal phase are included
This is considered to be because a phase having an intended crystal structure is generated by a peritectic reaction. M in the CaCu ₅ type crystal phase
g is scarcely present, and the MgCu ₂ type crystal phase is richer in Mg than the target crystal phase. Therefore, the hydrogen storage alloy has Mg segregation.

The present inventors have conducted intensive studies and found that Mg
It has been found that the degree of segregation affects the cycle life of the secondary battery. That is, if the area where the Mg concentration per unit area in the cross section is 0.5 to 2 times the average value thereof is less than 70%, the Mg segregation is large and the charge / discharge cycle life of the secondary battery is reduced. I do. It is presumed that a hydrogen storage alloy having a large Mg segregation has a region where corrosion oxidation by an alkaline electrolyte easily proceeds. When a sealed secondary battery is used, corrosion oxidation and insulation progress as the charge and discharge cycle progresses, and at the same time, a shortage of electrolyte (consumption) and an increase in the internal resistance of the secondary battery occur. Can not be obtained.

As described in the present invention, Mg segregation can be reduced by setting the region where the Mg concentration per unit area in the cross section corresponds to 0.5 to 2 times the average value thereof to 70% or more. In addition, the region that is subject to corrosion and oxidation by the alkaline electrolyte can be reduced, and the cycle life and discharge capacity can be improved.

Further, according to the first to third hydrogen storage alloys according to the present invention, various application fields (storage / transport of hydrogen, storage / transport of heat, thermo-mechanical equipment) in which other alloys have been used so far. Conversion of energy, separation and purification of hydrogen, separation of hydrogen isotope, battery using hydrogen as active material, catalyst in synthetic chemistry,
It is thought that the temperature sensor etc.) can be expanded further, and furthermore, it can lead to the development of a new field using hydrogen storage alloy. Thus, the hydrogen storage alloy of the present invention has significantly improved characteristics as compared with the conventional alloy, and is considered to have high industrial value.

In FIG. 1 described above, the separator is interposed between the positive electrode and the negative electrode and spirally wound and housed in a cylindrical container having a bottom. The secondary battery of the present invention has such a structure. It is not limited to. For example, the present invention can be similarly applied to a prismatic secondary battery in which a separator is interposed between a positive electrode and a negative electrode, and a laminate obtained by laminating a plurality of the separators is housed in a bottomed rectangular cylindrical container.

[0092]

Embodiments of the present invention will be described below in detail with reference to the drawings.

(Examples 1 to 13 and Comparative Examples 1 to 5) Each element was weighed so as to have the composition shown in Table 1 below, and an alloy ingot was obtained by high frequency melting under an argon atmosphere. Subsequently, each alloy ingot was subjected to a heat treatment at 960 ° C. for 12 hours in an argon atmosphere. Note that Mm in Table 1 is composed of 12% by weight of La, 60% by weight of Ce, 10% by weight of Pr, and 18% by weight of Nd.

The obtained hydrogen storage alloy was pulverized and sieved to obtain a hydrogen storage alloy powder having a particle size of not less than 20 μm and not more than 150 μm.

The obtained Examples 1 to 13 and Comparative Examples 1 to 5
Of hydrogen storage alloy powder of
The pressure-composition isotherm was measured under a hydrogen pressure of less than 10 atm and the hydrogen pressure at the time of releasing hydrogen at (H / M) = 0.8 was P ₁
And the hydrogen pressure at the time of hydrogen release at (H / M) = 0.2 is P ₂
Then, P ₂ / P ₁ was calculated, and the result is also shown in Table 1 below. Further, the hydrogen pressure at the time of storing hydrogen at (H / M) = 0.8 is P _A0.8 , the hydrogen pressure at the time of storing hydrogen at (H / M) = 0.2 is P _A0.2 , (H /M)=0.8 when the hydrogen pressure at the time of releasing hydrogen is _0.8 and the hydrogen pressure when releasing hydrogen at (H / M) = 0.2 is _PD0.2, and the ratio ｛( P _A0.2 / P
_D0.2 ) / (P _A0.8 / P _D0.8 )｝, and the results are shown in Table 1 below.

[0096]

[Table 1]

As is clear from Table 1, the above (1)
The hydrogen storage alloys of Examples 1 to 13 having the composition represented by the formula have smaller P ₂ / P ₁ than the hydrogen storage alloys of Comparative Examples 1 to 5, and have flatness of the equilibrium pressure during hydrogen storage and release. And the ratio {( _PA0.2 / _PD0.2 ) / ( _PA0.8 / _PD0.8 )}
It can be seen that the difference in the equilibrium pressure at the time of storing and releasing hydrogen can be reduced.

(Examples 14 to 18 and Comparative Examples 6 to 7) Each element was weighed so as to have the composition shown in Table 2 below, and an alloy ingot was obtained by high frequency melting under an argon atmosphere. Subsequently, each alloy ingot was subjected to a heat treatment at 950 ° C. for 12 hours in an argon atmosphere. In Table 2, Lm (1) is 97% by weight of La and 0.03% by weight of C
e, consisting of 0.07% by weight of Pr and 2% by weight of Nd, Lm (2) is 47% by weight of La, 2% by weight of Ce,
It consists of 13% by weight of Pr and 38% by weight of Nd.

The obtained hydrogen storage alloy was pulverized so as to have a particle size of 100 μm or less to obtain a hydrogen storage alloy powder.

Next, Examples 14 to 18 and Comparative Examples 6 to
For the hydrogen storage alloy No. 7, the hydrogen storage rate was measured using a temperature scanning type hydrogen storage and release characteristic evaluation apparatus shown in FIG.

FIG. 2 is a schematic view showing a temperature scanning type hydrogen storage / release characteristic evaluation apparatus used for evaluating a hydrogen storage alloy. The hydrogen cylinder 31 is connected to a sample container 33 through a pipe 32. The pipe 32 is branched on the way, and an end of the branch pipe 34 is connected to a vacuum pump 35. The pressure gauge 36 is attached to a pipe portion 34a further branched from the branch pipe 34.
Piping 32 between the hydrogen cylinder 31 and the sample container 33
The first and second valves 3 from the cylinder 31 side
7 _1, 37 ₂ is interposed. The accumulator 38 is connected to the pipe 32 between the _first and _second valves 37 ₁ and 37 ₂ . The vacuum pump 35 is connected to the branch pipes 34a through the third valve 37 _3. The heater 39 is attached to the sample container 33. The thermocouple 40 is inserted into the sample container 33. A temperature controller 42 controlled by a computer 41 is connected to the thermocouple 40 and the heater 39, and adjusts the temperature of the heater 39 based on the temperature detected from the thermocouple 40. The recorder 43 controlled by the computer 41 is connected to the pressure gauge 36 and the temperature controller 42.

The hydrogen storage alloy powders of Examples 14 to 18 and Comparative Examples 6 and 7 were stored in the sample container 33 (atmospheric temperature of 15 ° C.) shown in FIG. Closing the first valve 37 _1, second and third valves 37 _2, 37 ₃ Open, the vacuum pump 3
5 was operated to exhaust the air in the pipe 32, the branch pipe 34, and the accumulator 38. After closing the second and third valves 37 ₂ and 37 ₃ , the first valve 37 ₁ is opened to supply hydrogen from the hydrogen cylinder 31 to replace the inside of the pipe 32, the branch pipe 34, and the accumulator 38 with hydrogen. did. Subsequently, the first valve 37 ₁ is closed, and at this point, the pressure gauge 36 is closed.
The amount of hydrogen introduced was calculated from the pressure in the system indicated by. Subsequently, the second opening the valve 37 _2, hydrogen was supplied into the sample container 33, to monitor the temperature at the thermocouple 40. Thereafter, the temperature was controlled by the computer 41 and the temperature controller 42 so that the temperature in the sample container 33 was constant. At this time, the pressure change in the container 33 was detected by the pressure gauge 36 and recorded by the recorder 43.

Next, the amount of hydrogen (H / M) occluded in each of the hydrogen storage alloys up to one hour after the introduction of a fixed amount of hydrogen into the sample container 33 was determined by the pressure in the container 33. Calculated from detection of change. The results are shown in Table 2 below as a hydrogen storage rate (H / M · h ⁻¹ ) at 15 ° C.

Further, Examples 14 to 18 and Comparative Examples 6 to
A test cell equipped with an electrode containing the hydrogen-absorbing alloy powder of No. 7 as a negative electrode was assembled, and high-rate discharge characteristics were measured.

First, each alloy powder and electrolytic copper powder were mixed at a weight ratio of 1: 2, and 1 g of this mixture was added at 10 ton /
10 m in diameter by pressing for 5 minutes at a pressure of cm ²
m pellets were prepared. The pellet is sandwiched between nickel metal meshes, the periphery is spot-welded and pressure-welded, and the nickel lead wire is spot-welded to form an electrode (negative electrode).
Was prepared.

Each of the obtained negative electrodes was immersed in an 8 N aqueous potassium hydroxide solution together with a sintered nickel electrode as a counter electrode, and subjected to a charge / discharge test at 30 ° C. The charge and discharge conditions were 100 mA per gram of the hydrogen storage alloy.
After charging for 5 hours, the battery was paused for 10 minutes, and discharged at a current of 100 mA per 1 g of the hydrogen storage alloy until the voltage became -0.7 V with respect to the mercury oxide electrode. This charge / discharge cycle was repeated until the discharge capacity reached a constant value, and the discharge capacity at this time was defined as _Cmax . Then, it was left at 45 ° C. for 1 week in a discharged state. Then, C _max of 12
Discharge capacity C _3C when discharged at 3C after 0% charge
Was measured, to calculate the ratio of C _3C for _{C max (C 3C / C max} ), The results are also shown in Table 2 below.

[0107]

[Table 2]

As is clear from Table 2, the above (2)
It can be seen that the hydrogen storage alloys of Examples 14 to 18 having the compositions represented by the formulas have a higher hydrogen storage / release rate than the hydrogen storage alloys of Comparative Examples 6 and 7 having a smaller amount of Al.

Further, Examples 14 to 1 provided with the negative electrode containing the hydrogen storage alloy having the composition represented by the above formula (2)
The secondary battery of No. 8 has a higher capacity when discharged at a high rate after being left in a high-temperature environment, as compared with the secondary batteries of Comparative Examples 6 and 7 each including a negative electrode including a hydrogen storage alloy having a composition with a small amount of Al. It can be seen that the maintenance ratio is high.

(Examples 19 to 38 and Comparative Examples 8 to 10)
Each element is weighed so as to have a composition shown in Table 3 below,
The alloy was melted in a high frequency induction furnace under an argon atmosphere, poured into a water-cooled copper mold and solidified to obtain an alloy ingot. Subsequently, each alloy ingot was subjected to a heat treatment under the conditions shown in Table 4 below in an argon atmosphere. Lm (1) in Table 3 is 98
Wt% La, 0.02 wt% Ce, 0.08 wt%
Of Pr and 1% by weight of Nd, and Lm (2) is 48
Wt% La, 4 wt% Ce, 13 wt% Pr and 35 wt% Nd, Mm 38 wt% La,
47.3 wt% Ce, 5.5 wt% Pr, 9 wt%
Of Nd and 0.2% by weight of Sm.

The obtained Examples 19 to 38 and Comparative Examples 8 to
With respect to 10 hydrogen storage alloy ingots, the area amount where the Mg concentration per unit area in the cross section was 0.5 to 2.0 times the average value was measured, and the results are also shown in Table 4. This measuring method will be described using the hydrogen storage alloy of Example 29 as an example. A cross section of the hydrogen storage alloy ingot of Example 29 was magnified by an electron beam microanalyzer (EPMA) at a magnification of 20.
A backscattered electron image was taken at 0x. FIG. 3 shows the obtained backscattered electron image. Mg was mapped on the obtained backscattered electron image, the Mg count number (Mg concentration) per unit area was measured, and the area ratio of the cross section for each Mg count number was determined. FIG. 4 shows the results. Note that the horizontal axis in FIG. 4 is the Mg count number per unit area, and the vertical axis is the area ratio in the cross section. The average Mg count number per unit area was calculated from the Mg count number distribution diagram shown in FIG.
In this case, the average Mg count per unit area is 31
It was 5. Next, the actual count number and the average value were compared for each unit area, and the area amount in which the Mg count number per unit area was 0.5 to 2.0 times the average value was obtained.

In the hydrogen storage alloy of Example 29, the amount of the above-mentioned region was 99%, and as is apparent from the above-described reflected electron image of FIG. 3, it was found that there was almost no portion where Mg was segregated.

Next, Examples 19 to 38 and Comparative Examples 8 to
10 hydrogen storage alloy ingots were pulverized in an argon atmosphere so as to have an average particle size of 35 μm to obtain a hydrogen storage alloy powder.

Next, Examples 19 to 38 and Comparative Examples 8 to
The hydrogen storage rate (H / M · h ⁻¹ ) at 10 ° C. of the hydrogen storage alloy powder No. 10 was measured at 10 ° C. using the temperature scanning type hydrogen storage / release characteristic evaluation apparatus shown in FIG. 2 described above. It is shown in Table 5.

Further, Examples 19 to 38 and Comparative Examples 8 to
A test cell equipped with an electrode containing 10 hydrogen storage alloy powders as a negative electrode was assembled, and the discharge capacity and cycle life were measured.

First, each alloy powder and electrolytic copper powder were mixed at a weight ratio of 1: 3, and 1 g of this mixture was mixed with 10 ton /
10 m in diameter by pressing for 5 minutes at a pressure of cm ²
m pellets were prepared. The pellet is sandwiched between nickel metal meshes, the periphery is spot-welded and pressure-welded, and the nickel lead wire is spot-welded to form an electrode (negative electrode).
Was prepared.

Each of the obtained negative electrodes was immersed in an 8 N aqueous potassium hydroxide solution together with a sintered nickel electrode as a counter electrode, and a charge / discharge test was performed at 45 ° C. The charge and discharge conditions were 200 mA per gram of the hydrogen storage alloy.
After charging for 2.5 hours, the battery was paused for 10 minutes and discharged at a current of 200 mA per gram of the hydrogen storage alloy until the voltage became −0.7 V with respect to the mercury oxide electrode. Such a charge / discharge cycle is repeated, the maximum discharge capacity and the cycle life are measured, and the results are shown in Table 5 below. Here, the cycle life is defined as the number of cycles when the discharge capacity is reduced to 70% of the maximum discharge capacity.

Examples 19 to 38 and Comparative Examples 8 to 1
A sealed nickel-metal hydride secondary battery described below was assembled using the hydrogen storage alloy powder of No. 0.

To 100 parts by weight of each hydrogen storage alloy powder, 1 part by weight of polytetrafluoroethylene (PTFE), 0.2 parts by weight of sodium polyacrylate, 0.2 parts by weight of carboxymethyl cellulose and 50 parts by weight of water were added. The mixture was stirred to form a paste, applied to a perforated nickel-plated iron thin plate, and dried to prepare a coated plate. The coated plate was adjusted in thickness by a roll press and then cut to prepare a negative electrode having a hydrogen storage alloy amount of 8 g.

The capacity is 1500 mA according to a known technique.
h of the paste-type nickel positive electrode was produced.

An electrode group was formed by spirally winding the separator between the negative electrode and the positive electrode through a polyolefin nonwoven fabric on which acrylic acid was graft-polymerized.
The electrode group and 7 mol / L KOH, 0.5 mol / L
2.4 ml of an alkaline electrolyte composed of NaOH and 0.5 mol / L LiOH in a bottomed cylindrical container,
With a nominal capacity of 1500 mAh, AA
A sealed cylindrical nickel-metal hydride secondary battery having a size was assembled.

The obtained Examples 19 to 38 and Comparative Examples 8 to
After leaving the secondary battery of No. 10 at room temperature for 24 hours after sealing, the battery was charged at a current of 150 mA for 15 hours, and discharged and charged at a current of 150 mA until the battery voltage reached 0.8 V five times. Continued in the environment of 45 ℃ 1
The battery is charged with a current of 500 mA.
After charging by the -ΔV method, the battery is charged at a current of 1500 mA until the battery voltage reaches 1.0 V. The charge / discharge cycle is repeated until the discharge capacity reaches 70% of the initial capacity. The number of charge / discharge cycles before the decrease was measured, and the results are also shown in Table 5 below.

[0123]

[Table 3]

[0124]

[Table 4]

[0125]

[Table 5]

As is clear from Tables 3 to 5, it has a composition represented by the following general formula (3), and the Mg concentration per unit area in the cross section is 0.5 to 2 times the average value. It can be seen that the hydrogen storage alloys of Examples 19 to 38 in which the region is 70% or more have a higher hydrogen storage / release speed than the hydrogen storage alloys of Comparative Examples 8 to 10 in which the region is less than 70%.

In addition, hydrogen storage having a composition represented by the following general formula (3) and having a region where the Mg concentration per unit area is 0.5 to 2 times the average in the cross section is 70% or more. The secondary batteries of Examples 19 to 38 including the negative electrode including the alloy had higher discharge capacities than the secondary batteries of Comparative Examples 8 to 10 including the negative electrode including the hydrogen storage alloy in which the region was less than 70%. It can be seen that the charge and discharge cycle life is long.

[0128]

As described above in detail, according to the present invention, there is provided a hydrogen storage alloy having high flatness of equilibrium pressure at the time of hydrogen storage and release and a reduced pressure difference at the time of hydrogen storage and release. Can be provided. Further, according to the present invention, a hydrogen storage alloy having an improved hydrogen storage / release speed can be provided. Further, according to the present invention, a secondary battery having a high capacity and a long life can be provided. Further, according to the present invention, it is possible to provide a secondary battery in which the corrosion and oxidation of the hydrogen storage alloy by the alkaline electrolyte is suppressed, and the high-rate discharge characteristics are improved. Further, according to the present invention, it is possible to provide a secondary battery in which the corrosion and oxidation of the hydrogen storage alloy by the alkaline electrolyte is suppressed, and the discharge capacity and the charge / discharge cycle life are improved.

[Brief description of the drawings]

FIG. 1 is a partially cutaway perspective view showing an example of a secondary battery according to the present invention.

FIG. 2 is a schematic diagram showing a temperature scanning type hydrogen storage / release characteristic evaluation apparatus used in Examples.

FIG. 3 is a photograph of a metal structure shown in a reflected electron image of the hydrogen storage alloy of Example 29 taken at a magnification of 200 times with an electron beam microanalyzer (EPMA).

FIG. 4 is a characteristic diagram showing a distribution of a Mg count number in the hydrogen storage alloy of Example 29.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Container, 2 ... Positive electrode, 3 ... Separator, 4 ... Negative electrode, 5 ... Electrode group, 7 ... Sealing plate, 8 ... Insulating gasket.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hideki Yoshida 72 Horikawa-cho, Saiwai-ku, Kawasaki-shi, Kanagawa Pref. (72) Inventor Masaaki Yamamoto 72 Horikawa-cho, Saiwai-ku, Kawasaki-shi, Kanagawa F-term (reference) 5H003 AA02 AA03 AA04 BB02 BD00 BD04 5H028 AA02 AA05 AA06 EE01 FF02 HH00 HH01

Claims (6)

[Claims] 1. A hydrogen storage alloy having a composition represented by the following general formula (1). Mg _a (La _1−b R1 _b ) _1−a Ni _X Co _Y M1 _Z (1) where R1 is at least two kinds of elements selected from rare earth elements including Y, and R1 is a combination of R1 and La. Ce content is less than 20% by weight, M1 is M
n, Fe, V, Cr, Nb, Al, Ga, Zn, Sn,
At least one element selected from Cu, Si, P and B, and the atomic ratios a, b, X, Y and Z are each 0.15.
<A <0.35, 0.55 ≦ b ≦ 0.95, 0 ≦ Y ≦
1.5, 0 ≦ Z ≦ 0.2, 2.9 <X + Y + Z <3.5
Is defined as 2. A positive electrode, comprising a negative electrode containing a hydrogen storage alloy having a composition represented by the following general formula (1), a separator interposed between the positive electrode and the negative electrode, and an alkaline electrolyte. A secondary battery characterized by the above-mentioned. Mg _a (La _1−b R1 _b ) _1−a Ni _X Co _Y M1 _Z (1) where R1 is at least two kinds of elements selected from rare earth elements including Y, and R1 is a combination of R1 and La. Ce content is less than 20% by weight, M1 is M
n, Fe, V, Cr, Nb, Al, Ga, Zn, Sn,
At least one element selected from Cu, Si, P and B, and the atomic ratios a, b, X, Y and Z are each 0.15.
<A <0.35, 0.55 ≦ b ≦ 0.95, 0 ≦ Y ≦
1.5, 0 ≦ Z ≦ 0.2, 2.9 <X + Y + Z <3.5
Is defined as 3. A hydrogen storage alloy having a composition represented by the following general formula (2). Mg _a R2 _1-ab T1 _b Ni _ZXY Al _X M2 _Y (2) where R2 is at least one element selected from rare earth elements containing Y, and the La content is less than 55% by weight; Are Ca, Ti, Zr, Hf, Li, Na,
At least one element selected from the group consisting of K, Rb, Cs, Sr and Ba, and M2 is Co, Mn, Fe, Ga, Zn,
Sn, Cu, Si, B, Nb, W, Mo, V, Cr, T
a, P, and at least one element selected from S and the atomic ratios a, b, X, Y, and Z are each 0.1 ≦ a <0.
3, 0 ≦ b ≦ 0.3, 0.2 <X <0.7, 0.1 ≦ Y
≦ 3.0, 3.25 ≦ Z ≦ 4.5. 4. A positive electrode, a negative electrode including a hydrogen storage alloy having a composition represented by the following general formula (2), a separator interposed between the positive electrode and the negative electrode, and an alkaline electrolyte. A secondary battery characterized by the above-mentioned. Mg _a R2 _1-ab T1 _b Ni _ZXY Al _X M2 _Y (2) where R2 is at least one element selected from rare earth elements containing Y, and the La content is less than 55% by weight; Are Ca, Ti, Zr, Hf, Li, Na,
At least one element selected from the group consisting of K, Rb, Cs, Sr and Ba, and M2 is Co, Mn, Fe, Ga, Zn,
Sn, Cu, Si, B, Nb, W, Mo, V, Cr, T
a, P, and at least one element selected from S and the atomic ratios a, b, X, Y, and Z are each 0.1 ≦ a <0.
3, 0 ≦ b ≦ 0.3, 0.2 <X <0.7, 0.1 ≦ Y
≦ 3.0, 3.25 ≦ Z ≦ 4.5. 5. A method according to claim 1, wherein a region having a composition represented by the following general formula (3) and having a Mg concentration per unit area of 0.5 to 2 times the average value in the cross section is 70% or more. Characteristic hydrogen storage alloy. _{Mg a R3 1-ab T2 b} Ni ZX M3 X ... (3) However, R3 is at least one element selected from rare earth elements including Y, T2 is Ca, Ti, Zr and Hf
At least one element selected from the group consisting of Co, M
n, Fe, Al, Ga, Zn, Sn, Cu, Si, B,
At least one element selected from Nb, W, Mo, V, Cr, Ta, Li, P and S, and the atomic ratios a, b, X and Z are respectively 0.2 ≦ a ≦ 0.35 and 0 ≦ b. ≦ 0.
3, 0 <X ≦ 2.0, 3 ≦ Z ≦ 3.8. 6. A region having a composition having a composition represented by the following general formula (3) and having a Mg concentration per unit area of 0.5 to 2 times an average value in a cross section is 70% or more in a positive electrode. A secondary battery comprising: a negative electrode containing a hydrogen storage alloy as described above; a separator interposed between the positive electrode and the negative electrode; and an alkaline electrolyte. _{Mg a R3 1-ab T2 b} Ni ZX M3 X ... (3) However, R3 is at least one element selected from rare earth elements including Y, T2 is Ca, Ti, Zr and Hf
At least one element selected from the group consisting of Co, M
n, Fe, Al, Ga, Zn, Sn, Cu, Si, B,
At least one element selected from Nb, W, Mo, V, Cr, Ta, Li, P and S, and the atomic ratios a, b, X and Z are respectively 0.2 ≦ a ≦ 0.35 and 0 ≦ b. ≦ 0.
3, 0 <X ≦ 2.0, 3 ≦ Z ≦ 3.8.