JPH11323467A - Hydrogen storage alloy and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an alloy having good initial characteristics and improved characteristics of the discharging rate of a battery (rate characteristics), particularly in the low temp. high rate characteristics without deteriorating the characteristics of the service life (cycle characteristics) by composing the compsn. of an AB5 type alloy of the specified nonstoichiometric one (B site-rich) and allowing it to have a crystal structure of a CaCu5 type having a specified compsn. SOLUTION: This AB5 type hydrogen storage alloy having a crystal structure of a CaCu5 type expressed by the formula of MmNia Mnb Alc Cod Cue Vf is obtd. by heating and melting a hydrogen storage alloy raw material, subjecting it to casting and thereafter executing heat treatment in an inert gas atmosphere, and the heat treatment is executed under the heat treating conditions of 1000 to 1100 deg.C×1 to 6 hr. In the formula, Mm denotes misch metal, 3.95<=a<=4.3, 0.3<=b<=0.6, 0.15<=c<=0.5, 0<=d<=0.8, 0<=e<=0.3, 0.005<=f<=0.03 and 4.9<=a+b+d+d+e+f<=5.4 are satisfied, and (a) to (f) denote the molar number based on Mm 1 mol in either case.

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 a method for producing the same, and more particularly, to a hydrogen storage alloy having very good initial characteristics without deteriorating life characteristics (cycle characteristics).
And the discharge rate characteristics (rate characteristics) of the battery, particularly -40 to 0
The present invention relates to a hydrogen storage alloy with improved low-temperature high-rate characteristics at 1 ° C. (1-10C) and a method for producing the same.

[0002]

2. Description of the Related Art In recent years,
As a high-capacity alkaline storage battery that replaces a nickel-cadmium storage battery, a nickel-hydrogen storage battery using a hydrogen storage alloy for a negative electrode has attracted attention. At present, as the hydrogen storage alloy, a five-element hydrogen storage alloy of Mm (mish metal), which is a rare earth-based mixture, and Ni, Al, Mn, and Co is widely used.

[0003] This Mm-Ni-Mn-Al-Co alloy can form a negative electrode with a relatively inexpensive material as compared with a La-based alloy, has a long cycle life, and has a small internal pressure rise due to gas generated during overcharge. Since a nickel-metal hydride storage battery can be obtained, it is widely used as an electrode material.

[0004] Currently used Mm-Ni-Mn-A
The l-Co alloy suppresses the pulverization of the alloy and prolongs the cycle life. In general, however, in order to suppress the pulverization, about 10% by weight of Co (0.1% relative to 1 mol of misch metal) is used. 6 to 1.0). Further, in order to obtain excellent hydrogen storage characteristics and corrosion resistance, a certain amount of Co is required.

However, the higher the Co content, the higher the raw material cost, and this is regarded as a problem from the viewpoint of raw material cost. In particular, power supplies for electric vehicles (EV: Electric
For the application to large batteries such as vihicles) and the further increase in the market for nickel-hydrogen storage batteries, the raw material cost accounts for a large proportion in the selection of the electrode negative electrode material, which has been a problem.

[0006] To solve such a problem, Japanese Patent Application Laid-Open No. 9-213319 discloses Mm-Ni-Mn-Al.
-The composition of the Co-based alloy was changed, and
It has been proposed to add elements. By using the hydrogen storage alloy powder described in the publication for the negative electrode, it is possible to suppress the deterioration of the negative electrode due to the pulverization of the alloy to a certain extent and to prolong the cycle life of the battery even though the amount of Co is small.

However, when the hydrogen storage alloy disclosed in the above publication is used, there is a problem that stable and good initial characteristics cannot be obtained. Further, the pulverization characteristics and the hydrogen storage characteristics are not always satisfactory.

Further, as described above, the AB ₅ type hydrogen storage alloy is used in a large power source such as an EV, but its characteristics (initial characteristics, discharge rate characteristics) at 0 ° C. or less are not sufficient,
There is a problem in application to a large power supply such as V.

Accordingly, it is an object of the present invention to provide a battery having very good initial characteristics without deteriorating the life characteristics (cycle characteristics) and the discharge rate characteristics (rate characteristics) of the battery, especially -4.
An object of the present invention is to provide a hydrogen storage alloy having improved low-temperature high-rate characteristics (1-10C) at 0 to 0 ° C and a method for producing the same.

[0010]

The present inventors have SUMMARY OF THE INVENTION The result of various studies, the specific non-stoichiometry of the AB ₅ type alloy composition (B site rich), and hydrogen contained a certain amount of vanadium It has been found that the above object can be achieved by the occlusion alloy. In addition, it has been found that such a hydrogen storage alloy can be suitably obtained when the heat treatment conditions are constant in the above specific composition.

[0011] The present invention has been made based on the above findings, the general formula _{MmNi a Mn b Al c Co d} Cu e V f ( wherein, Mm is the mischmetal, 3.95 ≦ a ≦ 4.
3, 0.3 ≦ b ≦ 0.6, 0.15 ≦ c ≦ 0.5, 0 ≦
d ≦ 0.8, 0 ≦ e ≦ 0.3, 0.005 ≦ f ≦ 0.0
3, 4.9 ≦ a + b + c + d + e + f ≦ 5.4, provided that
a to f each have a CaCu ₅ type crystal structure represented by the following formula:
There is provided a B ₅ type hydrogen storage alloy.

The present invention also provides, as a preferred method for producing the hydrogen storage alloy of the present invention, a method of heating and melting a hydrogen storage alloy material, casting it, and then heat treating it in an inert gas atmosphere. A method for producing an AB ₅ type hydrogen storage alloy having a CaCu ₅ type crystal structure, wherein the heat treatment conditions are 1000 to 1100 ° C. for 1 to 6 hours. Is provided. Formula _{MmNi a Mn b Al c Co d} Cu e V f ( wherein, Mm is the mischmetal, 3.95 ≦ a ≦ 4.
3, 0.3 ≦ b ≦ 0.6, 0.15 ≦ c ≦ 0.5, 0 ≦
d ≦ 0.8, 0 ≦ e ≦ 0.3, 0.005 ≦ f ≦ 0.0
3, 4.9 ≦ a + b + c + d + e + f ≦ 5.4, provided that
a to f are moles per mole of Mm)

Further, as a preferred method for producing the hydrogen storage alloy of the present invention, the hydrogen storage alloy raw material is heated and melted, and this is rapidly quenched and solidified at a super quenching speed of 10 K ³ / sec or more. heat treatment, a method of manufacturing a AB ₅ type hydrogen storage alloy having a CaCu ₅ type crystal structure represented by the following general formula, the heat treatment conditions are 600
An object of the present invention is to provide a method for producing a hydrogen storage alloy, which is performed at 1000 ° C. for 10 minutes to 6 hours. Formula _{MmNi a Mn b Al c Co d} Cu e V f ( wherein, Mm is the mischmetal, 3.95 ≦ a ≦ 4.
3, 0.3 ≦ b ≦ 0.6, 0.15 ≦ c ≦ 0.5, 0 ≦
d ≦ 0.8, 0 ≦ e ≦ 0.3, 0.005 ≦ f ≦ 0.0
3, 4.9 ≦ a + b + c + d + e + f ≦ 5.4, provided that
a to f are moles per mole of Mm)

[0014]

Hydrogen storage alloy of the embodiment of the present invention have the general formula _{MmNi a Mn b Al c Co d} Cu e V f ( wherein, Mm is the mischmetal, 3.95 ≦ a ≦ 4.
3, 0.3 ≦ b ≦ 0.6, 0.15 ≦ c ≦ 0.5, 0 ≦
d ≦ 0.8, 0 ≦ e ≦ 0.3, 0.005 ≦ f ≦ 0.0
3, 4.9 ≦ a + b + c + d + e + f ≦ 5.4, provided that
a to f are AB ₅ type hydrogen storage alloys having a CaCu ₅ type crystal structure represented by the following formula:

Here, Mm is La, Ce, Pr, Nd,
Misch metal which is a mixture of rare earths such as Sm
You. Lanthanum content in this misch metal
Is 14 to 27% by weight in the hydrogen storage alloy. Also,
This hydrogen storage alloy is CaCu _FiveHas a type crystal structure
AB_FiveType hydrogen storage alloy, AB_4.9~_5.4B site
The non-stoichiometric composition of the switch.

In this hydrogen storage alloy, Ni _a Mn _b
Al _c Co _d Cu _e V (number of moles Mm1 mol) composition ratio of _f are those having the following relationship. That is, the ratio of Ni is 3.9 ≦ a ≦ 4.3, the ratio of Mn is 0.3 ≦ b ≦ 0.6, and the ratio of Al is 0.15.
≦ c ≦ 0.5, the proportion of Co is 0 ≦ d ≦ 0.8, the proportion of Cu is 0 ≦ e ≦ 0.3, and V is 0.00
5 ≦ f ≦ 0.03, and a + b + c + d + e + f
Is in the range of 4.9 to 5.4.

As described above, the proportion a of Ni is 3.9 to 3.9.
4.3, preferably 4.0 to 4.2, and a is 3.9
If it is less than 4.3, the hydrogen storage capacity is impaired, and if it exceeds 4.3, pulverization and deterioration of life characteristics are recognized, and the plateau pressure increases.

The ratio b of Mn is from 0.3 to 0.6, preferably from 0.35 to 0.4. If b is less than 0.3, the plateau pressure increases and the hydrogen storage capacity is impaired. .6
If it exceeds 300, corrosion of the alloy becomes severe and early deterioration of the alloy is recognized.

The proportion c of Al is 0.15 to 0.5,
If c is less than 0.15, the plateau pressure, which is the pressure at which the hydrogen storage alloy is released, increases, and the energy efficiency of charging and discharging deteriorates. If c exceeds 0.5, the hydrogen storage amount decreases.

The proportion d of Co is 0 to 0.8, preferably 0.4 to 0.75. If d exceeds 0.8, the proportion of Co increases and cost reduction cannot be achieved.

The proportion e of Cu is 0 to 0.3, preferably 0.
When e exceeds 0.3, the hydrogen storage properties are impaired and Cu may precipitate.

The ratio f of V is 0.005 to 0.03 (0.05 to 0.4% by weight on the basis of weight). By adding vanadium, the Pura-To pressure is reduced and the discharge rate (rate characteristic) of the battery is reduced. ) Characteristics, particularly discharge rate characteristics at low temperatures, can be improved. If f is less than 0.005, the pulley pressure does not decrease, and if it exceeds 0.03, the elution of aluminum increases, the pulverization characteristics are impaired, and vanadium is expensive, so that the economic efficiency is poor.

A + b + c + d + e + f (hereinafter sometimes collectively referred to as x) is 4.9 to 5.4, and x is 4.
If it is less than 9, the battery life and pulverization characteristics are impaired, and if it exceeds 5.4, the hydrogen storage characteristics are impaired.

Next, a method for producing the hydrogen storage alloy of the present invention will be described. First, the hydrogen storage alloy material is weighed and mixed so as to have the alloy composition as described above, and the hydrogen storage alloy material is melted to form a molten metal by using, for example, a high-frequency heating melting furnace by induction heating. . This is poured into a mold, for example, a water-cooled mold, and the hydrogen-absorbing alloy is poured into 1350.
Cast at １５1550 ° C. to produce a hydrogen storage alloy.

Next, the obtained hydrogen storage alloy is heat-treated in an inert gas atmosphere, for example, an argon gas. The heat treatment conditions are 1000 to 1100 ° C. for 1 to 6 hours. Such heat treatment is performed because the structure of the cast alloy usually has fine grain boundary segregation mainly composed of Mn, but is homogenized by heating.

Further, as another method for producing the hydrogen storage alloy of the present invention, a molten metal obtained by weighing and mixing the hydrogen storage alloy raw materials so as to have the alloy composition as described above is used. ³ K / sec or more, preferably 10 ³ to 10
^A hydrogen storage alloy is produced by an ultra-quenched solidification method of ultra-quench solidification at a rapid cooling rate of about ⁵ K / sec, specifically, a melt spin method, an atomizing method, a liquid dynamic compaction method, or the like.

Next, the obtained hydrogen storage alloy is heat-treated in an inert gas atmosphere, for example, in an argon gas in the same manner as described above. The heat treatment is performed at 600 to 1000 ° C. for 10 minutes to 6 hours.

[0028] Thus, it has good initial characteristics,
In addition, a hydrogen storage alloy having excellent discharge rate characteristics of a battery, particularly, low-temperature discharge rate characteristics can be obtained.

This hydrogen storage alloy is subjected to coarse pulverization and fine pulverization.
It is suitably used as a negative electrode of an alkaline storage battery. Such an alkaline storage battery has good initial characteristics, suppresses deterioration of the negative electrode due to pulverization of the alloy, and has a long cycle life.

[0030]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below based on embodiments and the like. The percentages in Table 1 are based on weight.

Example 1 Mm, Ni, Mn, Al, C
o, Cu and V with alloy composition MmNi _4.04 Mn _{0. 35} Al
_0.3 Co _0.4 Cu to become _{0.1 V 0.01 (x = 5.20)} , the respective hydrogen absorbing alloy materials weighed and mixed, and fixed to a high-frequency melting furnace and put the mixture in a crucible, 10 ^-4 to 10
^-5 Torr and then melted by heating in an argon gas atmosphere, then poured into a water-cooled copper mold,
Casting was performed at 0 ° C. to obtain an alloy. Further, this alloy was heat-treated at 1060 ° C. for 3 hours in an argon gas atmosphere to obtain a hydrogen storage alloy.

[Comparative Example 1] The alloy composition was MmNi _3.95 Mn.
_A hydrogen storage alloy was obtained in the same manner as in Example 1, except that each hydrogen storage alloy raw material was used so as to obtain _0.45 Al _0.3 Co _0.4 Cu _0.1 (x = 5.20).

Examples 2 to 14 Hydrogen storage alloys were obtained in the same manner as in Example 1 except that each hydrogen storage alloy raw material was used so that the alloy composition was as shown in Table 1.

Example 15 Mm, Ni, Mn, Al,
Co, Cu and V with alloy composition MmNi _3.95 Mn _{0. 45} A
l _0.3 Co _0.4 Cu _0.1 V _0.01 (x = 5.21) Each hydrogen storage alloy raw material is weighed and mixed, and the mixture is put in a crucible and fixed in a high-frequency melting furnace, and 10 ^-3 To
After vacuuming to rr, the mixture was heated and melted in an argon gas atmosphere, and then ultra-rapidly solidified by a melt spin method at a cooling rate of about 10 ³ to 10 ⁵ K / sec to obtain an alloy.
Further, the alloy was heated at 800 ° C. for 1 hour in an argon gas atmosphere.
Heat treatment was performed for a time to obtain a hydrogen storage alloy.

Example 16 and Comparative Example 2 A hydrogen storage alloy was obtained in the same manner as in Example 1 except that each hydrogen storage alloy raw material was used so that the alloy composition was as shown in Table 1.

[Characteristic evaluation] Examples 1 to 16 and Comparative Example 1
With respect to the hydrogen storage alloys obtained in Nos. 1 to 2, the micronization residual ratio and the aluminum elution amount were measured by the following methods. Table 2 shows the results.

<Residual rate of pulverization>
The process of introducing hydrogen gas of r into a hydrogen storage alloy adjusted to a particle size of 22 to 53 microns and then evacuating and evacuating 10 times is repeated, and then calculated by the ratio of the average particle size after the cycle test to the average particle size before the cycle test. did.

<Aluminum Dissolution Amount> An aluminum dissolution test was performed, and the test piece was treated with a 30% by weight aqueous KOH solution (75%).
C.) for 48 hours to perform ICP analysis.

[0039]

[Table 1]

[0040]

[Table 2]

As shown in Table 2, Examples 1 to 16
Was superior to Comparative Examples 1 and 2 in the degree of residual pulverization, and the aluminum elution amount was almost equal to or less than Comparative Examples 1 and 2.

Experimental Example 1 Examples 1 to 15 and Comparative Example 1
The hydrogen storage alloy obtained in the above was pulverized to obtain a hydrogen storage alloy powder, a negative electrode was prepared by a known method using the hydrogen storage alloy powder, and a nickel metal hydride battery was further prepared. The relationship between the number of cycles and the capacity of the storage battery thus obtained is shown in FIGS.

EXPERIMENTAL EXAMPLE 2 The hydrogen storage alloy obtained in Example 16 and Comparative Example 2 was pulverized into a hydrogen storage alloy powder,
Using this hydrogen storage alloy powder, a negative electrode was produced by a known method, and a nickel-metal hydride storage battery was produced. FIG. 6 shows the relationship between the number of cycles and the capacity of the storage battery obtained in this manner.

As is clear from the results shown in FIGS. 1 to 5, Examples 1 to 15 have a higher capacity for each cycle number than Comparative Example 1. Also, as is clear from the results of FIG.
Example 16 has a higher capacity for each cycle number than Comparative Example 2.

Experimental Example 3 Examples 1 to 15 and Comparative Example 1
Using the hydrogen storage alloy obtained in the above, a negative electrode was produced in the same manner as in Experimental Example 1, and a storage battery was produced. The storage battery thus obtained was charged at 0 ° C. and 0.2 C and at 0 ° C. and 1 C
7 to 11 show the relationship between the discharge capacity and the discharge voltage in discharging.

Experimental Example 4 Using the hydrogen storage alloys obtained in Example 16 and Comparative Example 2, a negative electrode was produced in the same manner as in Experimental Example 1, and a storage battery was produced. FIG. 12 shows the relationship between the discharge capacity and the discharge voltage at 0 ° C., 0.2 C charge and 0 ° C., 1 C discharge of the storage battery thus obtained.

7 to 11, Examples 1 to 15 are superior to Comparative Example 1 in discharge characteristics at a low temperature. In addition, as is clear from the results of FIG. 12, Example 16 is superior to Comparative Example 2 in discharge characteristics at a low temperature.

[0048]

As described above, the hydrogen storage alloy of the present invention has excellent initial characteristics without deteriorating the life characteristics (cycle characteristics), and has excellent discharge rate characteristics (rate characteristics) of the battery. The low-temperature high-rate characteristics (1-10C) of -40 to 0 ° C can be improved. In addition, the production method of the present invention enables the hydrogen storage alloy to be obtained stably and efficiently.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the number of cycles and the capacity of the storage batteries obtained in Examples 1 to 4 and Comparative Example 1.

FIG. 2 is a graph showing the relationship between the number of cycles and the capacity of the storage batteries obtained in Examples 5 to 8 and Comparative Example 1.

FIG. 3 is a graph showing the relationship between the number of cycles and the capacity of the storage batteries obtained in Examples 9 to 10 and Comparative Example 1.

FIG. 4 is a graph showing the relationship between the number of cycles and the capacity of the storage batteries obtained in Examples 11 to 13 and Comparative Example 1.

FIG. 5 is a graph showing the relationship between the number of cycles and the capacity of the storage batteries obtained in Examples 14 to 15 and Comparative Example 1.

FIG. 6 is a graph showing the relationship between the number of cycles and the capacity of the storage batteries obtained in Example 16 and Comparative Example 2.

FIG. 7 is a graph showing the relationship between the discharge capacity and the discharge voltage of the storage batteries obtained in Examples 1 to 4 and Comparative Example 1.

FIG. 8 is a graph showing the relationship between the discharge capacity and the discharge voltage of the storage batteries obtained in Examples 5 to 8 and Comparative Example 1.

FIG. 9 is a graph showing the relationship between the discharge capacity and the discharge voltage of the storage batteries obtained in Examples 9 to 10 and Comparative Example 1.

FIG. 10 is a graph showing the relationship between the discharge capacity and the discharge voltage of the storage batteries obtained in Examples 11 to 13 and Comparative Example 1.

FIG. 11 is a graph showing the relationship between the discharge capacity and the discharge voltage of the storage batteries obtained in Examples 14 to 15 and Comparative Example 1.

FIG. 12 is a graph showing the relationship between the discharge capacity and the discharge voltage of the storage batteries obtained in Example 16 and Comparative Example 2.

Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI // C22F 1/00 641 C22F 1/00 641A 661 661C 691 691B 691C

Claims (4)

[Claims] 1. A general formula _{MmNi a Mn b Al c Co d} Cu e V f ( wherein, Mm is the mischmetal, 3.95 ≦ a ≦ 4.
3, 0.3 ≦ b ≦ 0.6, 0.15 ≦ c ≦ 0.5, 0 ≦
d ≦ 0.8, 0 ≦ e ≦ 0.3, 0.005 ≦ f ≦ 0.0
3, 4.9 ≦ a + b + c + d + e + f ≦ 5.4, provided that
a to f each have a CaCu ₅ type crystal structure represented by the following formula:
B ₅ type hydrogen storage alloy. 2. An AB ₅ type hydrogen storage alloy having a CaCu ₅ type crystal structure represented by the following general formula, wherein a hydrogen storage alloy material is heated and melted, cast, and heat-treated in an inert gas atmosphere. , Wherein the heat treatment conditions are 1000 to 1100 ° C for 1 to 6 hours. Formula _{MmNi a Mn b Al c Co d} Cu e V f ( wherein, Mm is the mischmetal, 3.95 ≦ a ≦ 4.
3, 0.3 ≦ b ≦ 0.6, 0.15 ≦ c ≦ 0.5, 0 ≦
d ≦ 0.8, 0 ≦ e ≦ 0.3, 0.005 ≦ f ≦ 0.0
3, 4.9 ≦ a + b + c + d + e + f ≦ 5.4, provided that
a to f are moles per mole of Mm) 3. A hydrogen storage alloy material is heated and melted, solidified by rapid quenching at a rapid quenching speed of 10 K ³ / sec or more, and then heat-treated in an inert gas atmosphere to obtain CaCu ₅ represented by the following general formula. a method of manufacturing a AB ₅ type hydrogen storage alloy having a crystal structure of the mold, the heat treatment conditions are 600
A method for producing a hydrogen storage alloy, which is performed at 1000 ° C. for 10 minutes to 6 hours. Formula _{MmNi a Mn b Al c Co d} Cu e V f ( wherein, Mm is the mischmetal, 3.95 ≦ a ≦ 4.
3, 0.3 ≦ b ≦ 0.6, 0.15 ≦ c ≦ 0.5, 0 ≦
d ≦ 0.8, 0 ≦ e ≦ 0.3, 0.005 ≦ f ≦ 0.0
3, 4.9 ≦ a + b + c + d + e + f ≦ 5.4, provided that
a to f are moles per mole of Mm) 4. The method for producing a hydrogen storage alloy according to claim 3, wherein the ultra-quick solidification is performed by a melt spin method or an atomizing method.