JP3114677B2 - Hydrogen storage alloy and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydrogen storage alloy and a method for producing the same, and more particularly, to an alloy having a very small content of cobalt, excellent pulverization characteristics and hydrogen storage characteristics (PCT characteristics), and The present invention relates to a hydrogen storage alloy having good initial activity 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 the 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. Generally, however, to suppress the pulverization, about 10% by weight of Co (at an atomic ratio of 0.6 to 1. 0) is known. 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, the deterioration of the negative electrode due to the pulverization of the alloy can be suppressed to a certain extent and the cycle life of the battery can be prolonged despite the small amount of Co.

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.

[0008] Accordingly, an object of the present invention is to reduce the production cost by extremely reducing the content of cobalt, and to excel in pulverization and hydrogen storage properties.
An object of the present invention is to provide a hydrogen storage alloy having good initial characteristics and a method for producing the same.

[0009]

The present inventors have SUMMARY OF THE INVENTION The result of various studies, and the AB ₅ type alloy composition certain non-stoichiometric composition (B site rich), and the c-axis is in a predetermined range It has been found that the above object can be achieved by a hydrogen storage alloy. In addition, it has been found that such a hydrogen storage alloy can be obtained when the casting temperature and the heat treatment conditions have a certain relationship in the above specific composition.

[0010] The present invention has been made based on the above findings, the general formula _{MmNi a Mn b Al c Co d} Cu e ( wherein, Mm is the mischmetal, 3.9 ≦ a ≦ 4.0,
0.35 ≦ b ≦ 0.50, 0.25 ≦ c ≦ 0.4, 0.
3 ≦ d ≦ 0.5, 0.05 ≦ e ≦ 0.3, 5.15 ≦ a
+ B + c + d + e ≦ 5.35) An AB ₅ type hydrogen storage alloy having a CaCu ₅ type crystal structure represented by the formula: wherein the c-axis lattice length is 406.2 to 40.
An object of the present invention is to provide a hydrogen storage alloy having a hydrogen absorption rate of 6.9 pm.

Further, the present invention provides a preferred method for producing the hydrogen storage alloy of the present invention, in which a hydrogen storage alloy material is heated and melted, cast, and then heat-treated in an inert gas atmosphere. A method of producing an AB ₅ type hydrogen storage alloy having a CaCu ₅ type crystal structure, wherein the casting temperature is 1350 to 1550 ° C. and the heat treatment condition is 10
It is intended to provide a method for producing a hydrogen storage alloy, which is performed at 20 to 1100 ° C. for 3 to 6 hours. Formula _{MmNi a Mn b Al c Co d} Cu e ( wherein, Mm is the mischmetal, 3.9 ≦ a ≦ 4.0,
0.35 ≦ b ≦ 0.50, 0.25 ≦ c ≦ 0.4, 0.
3 ≦ d ≦ 0.5, 0.05 ≦ e ≦ 0.3, 5.15 ≦ a
+ B + c + d + e ≦ 5.35)

[0012]

Hydrogen storage alloy of the embodiment of the present invention have the general formula _{MmNi a Mn b Al c Co d} Cu e ( wherein, Mm is the mischmetal, 3.9 ≦ a ≦ 4.0,
0.35 ≦ b ≦ 0.50, 0.25 ≦ c ≦ 0.4, 0.
3 ≦ d ≦ 0.5, 0.05 ≦ e ≦ 0.3, 5.15 ≦ a
+ B + c + d + e ≦ 5.35) An AB ₅ type hydrogen storage alloy having a CaCu ₅ type crystal structure represented by the following formula:

Here, Mm is La, Ce, Pr, Nd,
It is a misch metal that is a rare earth-based mixture such as Sm. Further, this hydrogen storage alloy is an AB ₅ type hydrogen storage alloy having a CaCu ₅ type crystal structure, and AB _{5.15 to} AB
_5.35 B-site rich non-stoichiometric composition.

In this hydrogen storage alloy, Ni _a Mn _b
The composition ratio (atomic ratio) of Al _c Co _{d C e} has the following relationship. That is, the ratio of Ni is 3.9.
≦ a ≦ 4.0, and the ratio of Mn is 0.35 ≦ b ≦ 0.
50, the proportion of Al is 0.25 ≦ c ≦ 0.4, the proportion of Co is 0.3 ≦ d ≦ 0.5, and the proportion of Cu is 0.05 ≦ e ≦ 0.3. Yes, and a + b + c + d
+ E is in the range of 5.15 to 5.35.

As described above, the ratio a of Ni is 3.9 to 3.9.
When a is less than 3.9, the amount of hydrogen occlusion is impaired, and when it exceeds 4.0, a single phase is not formed and pulverization and deterioration in life characteristics are observed.

The ratio b of Mn is 0.35 to 0.50. If b is less than 0.35, the plateau pressure increases and the hydrogen storage capacity is impaired. If it exceeds 0.50, corrosion of the alloy becomes severe. And early deterioration of the alloy is observed.

The proportion c of Al is 0.25 to 0.4,
If c is less than 0.25, 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 0.4, the hydrogen storage amount decreases.

The ratio d of Co is 0.3 to 0.5,
Is less than 0.3, it is inferior in hydrogen storage properties and pulverization properties,
If it exceeds 0.5, the proportion of Co increases, and the cost cannot be reduced.

The proportion e of Cu is 0.05-0.3,
When e is less than 0.05, no improvement in the pulverization properties is observed,
If it exceeds 0.3, the hydrogen storage properties may be impaired, and Cu may precipitate.

A + b + c + d + e (hereinafter sometimes collectively referred to as x) is 5.15 to 5.35, and x is 5.
If it is less than 15, the battery life and pulverization characteristics are impaired, and 5.3
If it exceeds 5, the hydrogen storage properties will be impaired.

The hydrogen storage alloy of the present invention has a c-axis lattice length of 406.2 pm or more, preferably 406.2 to 406.
9 pm. When the lattice length of the c-axis is less than 406.2 pm, not only the pulverization characteristics are inferior, but also the initial characteristics (relative susceptibility) are reduced. Further, a hydrogen storage alloy having a diameter exceeding 406.9 pm involves difficulty in production and involves a significant decrease in the amount of hydrogen storage.

The lattice length of the c-axis of this hydrogen storage alloy is a +
There is a preferred value depending on the value of b + c + d + e (x), and when x is less than 5.15 to 5.25, the lattice length of c axis is preferably less than 406.2 to 406.5 pm;
When x is 5.25 to 5.35, the lattice length of the c-axis is preferably 406.5 to 406.9 pm.

Further, the lattice length of the a-axis of the hydrogen storage alloy of the present invention is not particularly limited, but generally ranges from 500.3 to 50.3.
01.0 pm.

Next, a method for producing the hydrogen storage alloy of the present invention will be described. First, the hydrogen storage alloy raw material is weighed and mixed so as to have the alloy composition as shown above, for example, using a high-frequency heating melting furnace by induction heating, melting the hydrogen storage alloy raw material to form a molten metal, This is poured into a mold, for example, a water-cooled mold, and the hydrogen-absorbing alloy is added to 1350-1.
Cast at 550 ° C.

Next, the obtained hydrogen storage alloy is heat-treated in an inert gas atmosphere, for example, an argon gas. The heat treatment conditions are 1020 to 1100 ° C for 3 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.

The casting temperature and the heat treatment temperature are also a + b
There is a preferred value depending on the value of + c + d + e (x),
When x is less than 5.15 to 5.25, the casting temperature is preferably 1350 to 1530 ° C, and the heat treatment temperature is preferably 1
040 to 1080C, and when x is 5.25 to 5.35, the casting temperature is preferably 1430 to 1550C, and the heat treatment temperature is preferably 1060 to 1100C.

In this way, a hydrogen storage alloy having excellent pulverization characteristics and hydrogen storage characteristics and excellent initial characteristics can be obtained despite the reduced content of cobalt.

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.

[0029]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below based on embodiments and the like.

[Examples 1-1 to 1-3 and Comparative Example 1-1]
1-4] Mm, Al, Mn, Co, Ni and Cu in alloy composition of MmAl _0.3 Mn _0.45 Co _0.4 Ni _3.95 Cu
Each hydrogen storage alloy material is weighed and mixed so that _0.1 (x = 5.20), and the mixture is put in a crucible and 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, it was poured into a water-cooled copper mold and cast at 1520 ° C. to obtain an alloy. Further, this alloy was heat-treated in an argon gas atmosphere under the conditions shown in Table 1 to obtain a hydrogen storage alloy. In Comparative Example 1-1, no heat treatment was performed.

[Examples 2-1 to 2-4 and Comparative Example 2-1]
~ 2-3] A hydrogen storage alloy was obtained in the same manner as in Example 1-1, except that the casting temperature was 1430 ° C and the heat treatment was performed under the conditions shown in Table 1. In Comparative Example 2-1, no heat treatment was performed.

[Examples 3-1 to 3-4 and Comparative Example 3-1]
~ 3-3] A hydrogen storage alloy was obtained in the same manner as in Example 1-1, except that the casting temperature was 1350 ° C and the heat treatment was performed under the conditions shown in Table 1. In Comparative Example 3-1, no heat treatment was performed.

Comparative Examples 4 to 6 Hydrogen storage alloys were obtained in the same manner as in Example 1-1, except that the casting temperature was set to the temperature shown in Table 1 and the heat treatment conditions were changed to 1060 ° C. for 3 hours.

[Examples 7-1 to 7-3 and Comparative Example 7-
1] Mm, Al, Mn, Co, Ni and Cu in alloy composition of Mm (Al _0.3 Mn _0.45 Co _0.4 Ni _3.95 Cu _0.1 )
Each hydrogen storage alloy raw material is weighed and mixed so that _y (y = 1.03, x = 5.35), and the mixture is placed in a crucible and fixed in a high-frequency melting furnace, and 10 ⁻⁴ to 10 ^{−. 5} Torr
After vacuuming until then, the mixture was heated and melted in an argon gas atmosphere, poured into a water-cooled copper mold, and cast at 1380 ° C. to obtain an alloy. Further, this alloy was heat-treated in an argon gas atmosphere under the conditions shown in Table 2 to obtain a hydrogen storage alloy.

Examples 8-1 to 8-4 and Comparative Example 8-
1] A hydrogen storage alloy was obtained in the same manner as in Example 7-1 except that the casting temperature was 1460 ° C and the heat treatment was performed under the conditions shown in Table 2.

Examples 9 to 12 and Comparative Examples 9 to 10 The alloy compositions were changed to Mm (Al _0.3 Mn _0.45 Co _0.4 N
i _3.95 Cu _0.1 ) _y (y = 0.97, x = 5.05)
(Comparative Example _{9), Mm (Al 0.3 Mn} 0.45 Co 0. 4 Ni
_3.95 Cu _0.1 ) _y (y = 0.98, x = 5.10) (Comparative Example 10), Mm (Al _0.3 Mn _0.45 Co _0.4 Ni _3.95)
Cu _0.1 ) _y (y = 0.99, x = 5.15) (Example 9), Mm (Al _0.3 Mn _0.45 Co _0.4 Ni _3.95 Cu
_0.1 ) _y (y = 1.01, x = 5.25) (Example 1)
0), Mm (Al _0.3 Mn _0.45 Co _0.4 Ni _3.95 Cu
_0.1 ) _y (y = 1.02, x = 5.30) (Example 1)
1), Mm (Al _0.3 Mn _0.45 Co _0.4 Ni _3.95 Cu
_0.1 ) _y (y = 1.03, x = 5.35) (Example 1)
A hydrogen storage alloy was obtained in the same manner as in Example 2-2, except that 2) was used.

[Characteristics Evaluation] The hydrogen storage alloys obtained in Examples and Comparative Examples were subjected to PCT by the following method.
The capacity, relative susceptibility, and residual ratio of pulverized powder were measured. The evaluations of these examples and comparative examples are based on the conventional Co10
The PCT capacity of the hydrogen storage alloy containing 0.8% by weight is 0.82 to 0.5%.
83, since the residual ratio of pulverization is 0.90 to 0.91,
Judgment was made based on this value. Tables 1 and 2 show the results.

<PCT capacity> Calculated from the storage characteristics measured at 45 ° C. H / M: 0 to 0.5 MPa

<Relative magnetic susceptibility> The hydrogen storage alloy was pulverized into a powder, and the powder was subjected to a surface treatment to measure the magnetization caused by the remaining Ni and Co. The ratio to the magnetization of the hydrogen storage alloy powder containing 10% by weight of Co was determined. Was calculated.

<Remaining rate of pulverization>
After introducing the hydrogen gas of r into a hydrogen storage alloy adjusted to a particle size of 22 to 35 microns and then devolatilizing and discarding 10 times, calculate the ratio of the average particle size after the cycle test to the average particle size before the cycle test. did.

[0041]

[Table 1]

[0042]

[Table 2]

As is clear from the results of Tables 1 and 2, the PCT capacity and the pulverization residual ratio of the examples are higher than those of the comparative examples, and are almost the same level as the conventional hydrogen storage alloy containing 10% by weight of Co. In addition, since the examples have higher relative susceptibility than the comparative examples, it can be seen that the examples have excellent initial characteristics.

[0044]

As described above, the hydrogen storage alloy of the present invention has a very low cobalt content, so that the production cost is reduced, and the hydrogen storage alloy is excellent in pulverization characteristics and hydrogen storage characteristics, and has good initial characteristics. Have. In addition, the production method of the present invention enables the hydrogen storage alloy to be obtained stably and efficiently.

────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI C22F 1/00 691 C22F 1/00 691C 1/10 1/10 Z H01M 4/38 H01M 4/38 A (72) Inventor Uchiyama Aro 1-5-1, Shiomachi, Takehara-shi, Hiroshima Mitsui Metal Mining Co., Ltd. Battery Materials Research Laboratory (72) Inventor Yoshiki Sakaguchi 1-5-1, Shiomachi, Takehara-shi, Hiroshima Pref. Mitsui Metal Mining Co., Ltd. Battery Materials Research Laboratory (72 ) Inventor: Shigeki Nakayama 1333-2, Hara-shi, Ageo-shi, Saitama Mitsui Mining & Smelting Co., Ltd. (56) References JP-A-7-286225 (JP, A) JP-A-9-213319 (JP, A) ( 58) Field surveyed (Int. Cl. ⁷ , DB name) C22C 19/00 C22C 1/00 H01M 4/38

Claims (7)

(57) [Claims] 1. A general formula _{MmNi a Mn b Al c Co d} Cu e ( wherein, Mm is the mischmetal, 3.9 ≦ a ≦ 4.0,
0.35 ≦ b ≦ 0.50, 0.25 ≦ c ≦ 0.4, 0.
3 ≦ d ≦ 0.5, 0.05 ≦ e ≦ 0.3, 5.15 ≦ a
+ B + c + d + e ≦ 5.35) An AB ₅ type hydrogen storage alloy having a CaCu ₅ type crystal structure represented by the following formula, wherein the c-axis lattice length is 406.2 pm or more. 2. The lattice length of the c-axis is 406.2 to 40.
The hydrogen storage alloy according to claim 1, wherein the hydrogen storage alloy is 6.9 pm. 3. In the above general formula, a + b + c + d +
The hydrogen storage alloy according to claim 1, wherein e is less than 5.15 to 5.25, and the lattice length of the c-axis is less than 406.2 to 406.5 pm. 4. In the above general formula, a + b + c + d +
e is 5.25 to 5.35 and the c-axis lattice length is 4
The hydrogen storage alloy according to claim 1, wherein the hydrogen storage alloy has a particle diameter of 06.5 to 406.9 pm. _5. 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 casting temperature is 1
350 to 1550 ° C, the heat treatment condition is 1020 to 110
A method for producing a hydrogen storage alloy, which is performed at 0 ° C. for 3 to 6 hours. Formula _{MmNi a Mn b Al c Co d} Cu e ( wherein, Mm is the mischmetal, 3.9 ≦ a ≦ 4.0,
0.35 ≦ b ≦ 0.50, 0.25 ≦ c ≦ 0.4, 0.
3 ≦ d ≦ 0.5, 0.05 ≦ e ≦ 0.3, 5.15 ≦ a
+ B + c + d + e ≦ 5.35) 6. In the above general formula, a + b + c + d +
e is less than 5.15 to 5.25, and the casting temperature is 1
350 to 1530 ° C, the heat treatment condition is 1040 to 108
The method for producing a hydrogen storage alloy according to claim 5, wherein the temperature is 0 ° C for 3 to 6 hours. 7. In the above general formula, a + b + c + d +
e is 5.25 to 5.35 and the casting temperature is 143
0 to 1550 ° C., and the heat treatment condition is 1060 to 1100
The method for producing a hydrogen storage alloy according to claim 5, wherein the temperature is 3 ° C for 3 to 6 hours.