JP2000038630A - Hydrogen storage alloy and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain good initial characteristics and the discharging ratio characteristics of a battery by preparing an alloy composed of specified ratios of Mm(mish metal), Ni, Mn, Al, Co, Cu and Ti and having a CaCu5 type crystal structure. SOLUTION: An AB5 type hydrogen storage alloy expressed by the general formula of MmNiaMnbAlcCodCueTif (in the formula, Mm denotes misch metal, and 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<=0.05 and 4.9<=a+b+c+d+f<=5.4 are satisfied, where each (a) to (f) denotes the molar number to mol of Mm) and having a CaCu5 type crystal structure is prepd. Moreover, this alloy can be obtd. by melting the raw material to form the above alloy compsn. by induction heating to form into metallic molten metal, flowing that into a mold, executing casting at about 1,350 to 1,550 deg.C and subjecting the obtd. hydrogen storage alloy to heat treatment at 1,000 to 1,100 deg.C for 1 to 6 hr in an inert gas atmosphere.

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 a small amount of cobalt, excellent initial characteristics without deteriorating life characteristics (cycle characteristics), and excellent discharge rate characteristics (rate characteristics) of a battery. An object of the present invention is to provide a hydrogen storage alloy having improved low-temperature high-rate characteristics (1-10C) of -40 to 0 ° C and a method for producing the same.

[0010]

As a result of various studies, the present inventors have found that the composition of the AB ₅ type alloy is a specific non-stoichiometric composition (B-site rich) and hydrogen containing a certain amount of titanium is contained. 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 Ti 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
5, 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 Ti 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
5, 4.9 ≦ a + b + c + d + e + f ≦ 5.4, provided that
a to f are moles per mole of Mm)

[0013]

Hydrogen storage alloy of the embodiment of the present invention have the general formula _{MmNi a Mn b Al c Co d} Cu e Ti 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
5, 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 Ti (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 0.1
5 ≦ c ≦ 0.5, the proportion of Co is 0 ≦ d ≦ 0.8, the proportion of Cu is 0 ≦ e ≦ 0.3, and V is 0.0
05 ≦ f ≦ 0.05, 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 proportion f of Ti is 0.005 to 0.05, and the addition of titanium lowers the Pura-Tau pressure and improves the discharge rate (rate characteristic) characteristics of the battery, particularly the low-temperature discharge rate characteristics. Can be. If f is less than 0.005, no improvement in discharge characteristics at low temperatures is observed, and 0.05
If it exceeds 300, the pulverization characteristics are impaired.

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.

In this way, 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.

The 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.

[0027]

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 Ti in alloy composition Mm (La 19% by weight)
Ni _3.95 Mn _0.45 Al _0.3 Co _0.4 Cu _0.1 Ti _0.005
Each hydrogen storage alloy material was weighed and mixed so that (x = 5.205), and the mixture was placed in a crucible, fixed in a high-frequency melting furnace, and evacuated to 10 ^-4 to 10 ^-5 Torr. Then, after heating and melting in an argon gas atmosphere, the mixture was poured into a water-cooled copper mold and cast at 1430 ° C. to obtain an alloy. Further, this alloy was placed in an argon gas atmosphere for 10 minutes.
Heat treatment was performed at 60 ° C. for 3 hours to obtain a hydrogen storage alloy.

[0029] [Comparative Example 1] Alloy composition Mm (La19 _{wt%) Ni 3.95 Mn 0.45 Al 0.3} Co 0.4 Cu 0. 1 (x
= 5.20), except that each hydrogen storage alloy raw material was used to obtain a hydrogen storage alloy in the same manner as in Example 1.

[Examples 2 to 6] 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.

[Characteristics Evaluation] The hydrogen storage alloys obtained in Examples 1 to 6 and Comparative Example 1 were measured for the pulverization residual ratio and the aluminum elution amount by the following methods. Table 2 shows the results.

<Remaining ratio of pulverization> 30 ba
The hydrogen gas of r is introduced into a hydrogen storage alloy adjusted to a particle size of 22 to 53 microns, the occlusion is performed, and then the process of evacuating and evacuating is repeated 10 times. Calculated by ratio.

<Aluminum Dissolution Amount> An aluminum dissolution test was performed.
C.) for 48 hours to perform ICP analysis.

[0034]

[Table 1]

[0035]

[Table 2]

As shown in Table 2, Examples 1 to 6
It can be seen that although the pulverization residual ratio is almost the same as that of Comparative Example 1, the elution amount of aluminum is suppressed.

EXPERIMENTAL EXAMPLE 1 The hydrogen storage alloys obtained in Examples 1 to 6 and Comparative Example 1 were pulverized into a hydrogen storage alloy powder, and a negative electrode was produced by a known method using the hydrogen storage alloy powder. Then, a nickel-metal hydride storage battery was produced. The storage battery thus obtained was charged at 0 ° C., 0.2 C, and 120%, and after a rest for 30 minutes, was strongly discharged at 0 ° C., 2 C, and 1 minute. The discharge characteristics at this time are shown in FIGS.
1 and 2, the horizontal axis represents time (minutes) and the vertical axis (V) represents voltage.

As shown in FIGS.
It can be seen that, compared to Comparative Example 1, the voltage drop with time was small and the low-temperature characteristics were good.

[0039]

As described above, the hydrogen storage alloy of the present invention has a low cobalt content, has very good initial characteristics without deteriorating the life characteristics (cycle characteristics), and has excellent discharge characteristics. Rate characteristics (rate characteristics), especially -4
The low-temperature high-rate characteristics (1-10C) of 0 to 0 ° C. can be improved. Further, according to the production method of the present invention,
The hydrogen storage alloy can be obtained stably and efficiently.

[Brief description of the drawings]

FIG. 1 is a graph showing the discharge characteristics of a storage battery obtained in Examples 1 to 4 and Comparative Example 1 at 0 ° C. and a discharge rate of 2C.

FIG. 2 is a graph showing the discharge characteristics of the storage batteries obtained in Examples 5 to 6 and Comparative Example 1 at 0 ° C. and a discharge rate of 2C.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C22F 1/00 661 C22F 1/00 661C 691 691B 691C (72) Inventor Kiyotaka Yasuda 1-chome Shiomachi, Takehara City, Hiroshima Prefecture No.5-1 F-term in the Materials Research Laboratories of Mitsui Kinzoku Mining Co., Ltd. 5H003 AA02 AA04 BA01 BB02 BC06 BD00 BD01

Claims (2)

[Claims] 1. A general formula _{MmNi a Mn b Al c Co d} Cu e Ti 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
5, 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 Ti 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
5, 4.9 ≦ a + b + c + d + e + f ≦ 5.4, provided that
a to f are moles per mole of Mm)