JPH07320739A - Hydrogen storage alloy electrode - Google Patents

Abstract

PURPOSE:To provide a hydrogen storage alloy electrode capable of sufficiently charging and obtaining high capacity over a wide temperature range. CONSTITUTION:A hydrogen storage alloy is used as an active material. The hydrogen storage alloy has a composition of LaNi4.0AlxCo1.0-x(0.4<=x<=0.9) or LaNi3.6gAlxCo1.4-x(0.2<=x<=0.8).

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a hydrogen storage alloy electrode used as a negative electrode of an alkaline storage battery.

[0002]

2. Description of the Related Art As an alkaline storage battery using a hydrogen storage alloy as a negative electrode material, a dry battery type is known. This dry battery type alkaline storage battery has an operating temperature range of 0 to 40.
Since it is as low as ℃, it is mainly used as an indoor storage battery.

In recent years, attempts have been made to increase the size of alkaline storage batteries and mount them on electric vehicles. In this case, since the alkaline storage battery is used outdoors, it is desired that it can be used in a wider temperature range. Therefore, the hydrogen storage alloy electrode is also required to be usable in a wide temperature range. In addition, when the alkaline storage battery is mounted on an electric vehicle, it is desirable to make it a sealed type in consideration of safety and convenience. In this case, the alkaline storage battery is required to have a low hydrogen equilibrium pressure in order to suppress an increase in internal pressure. In addition, in order to prevent hydrogen gas and oxygen gas from being generated during overcharge and increase in internal pressure, a catalyst function is required to react the generated oxygen gas and hydrogen gas and return them to water.

Conventionally, as a hydrogen storage alloy electrode which can be used in a wide temperature range, JP-A-60-212958 discloses an electrode using a multilayer structure composed of LaNi ₅ and CaNi ₅ . This hydrogen storage alloy electrode can be used in a temperature range of -30 to 40 ° C by using together hydrogen storage alloys having different usable temperature ranges.

Further, Japanese Patent Publication No. 58-39217 discloses a hydrogen storage alloy electrode using a hydrogen storage alloy using Mm (Misch metal) as an active material. This hydrogen storage alloy electrode realizes a long life.

[0006]

However, the hydrogen storage alloy electrode using the multilayer structure uses an alloy such as CaNi ₅ in which the melting points of the respective elements are greatly different. In the case of manufacturing, the element on the low melting point side is vaporized and the composition ratio changes, which makes manufacturing difficult.
Moreover, since a plurality of types of hydrogen storage alloys are handled, the manufacturing process becomes complicated. Further, a storage battery using an electrode made of LaNi ₅ has a short cycle life, which causes a problem in use.

On the other hand, in the hydrogen storage alloy electrode using the hydrogen storage alloy containing Mm, the plateau pressure of the hydrogen storage alloy containing Mm, that is, the graphs showing the relationship between the hydrogen dissociation ratio and the pressure shown in FIGS. 10 and 11. The pressure in the plateau regions 30 and 40 is MmNi _4.0 Al _0.4 Co.
_In the case of _0.6 , 2 to 3 atm, MmNi _3.6 Al _0.4 Co
_Since it is relatively high at 5 atm in the case of _1.0 , unless the internal pressure of the storage battery is increased, hydrogen is generated before the metal hydride is formed, so the storage battery cannot be hermetically sealed. It cannot be fully charged. Also,
The hydrogen storage alloy containing Mm has large self-discharge even when the internal pressure of the battery is normal pressure, and cannot be used as an electrode.

The present invention has been made in view of the above points, and when it is used in an alkaline storage battery, it can be sufficiently charged, a sufficient discharge capacity can be obtained in a wide temperature range, and the storage battery can be obtained. It is an object of the present invention to provide a hydrogen storage alloy electrode which can be easily sealed and has a sufficient cycle life.

[0009]

The first invention of the present invention is as follows:
In an electrode using a hydrogen storage alloy as an active material, the hydrogen storage alloy is LaNi _4.0 Al _x Co _1.0-x (0.4 ≦ x ≦
Provided is a hydrogen storage alloy electrode having a composition of 0.9).

A second aspect of the present invention is an electrode using a hydrogen storage alloy as an active material, wherein the hydrogen storage alloy is L.
To provide a hydrogen storage alloy electrode, characterized by having a composition of _{aNi 3.6 Al y Co 1.4-y} (0.2 ≦ y ≦ 0.8).

Here, in the first invention, LaNi is used.
_{X in 4.0} Al _x Co _1.0- x is 0.4 ≦ x ≦ 0.9.
It is necessary to set in the range of. This is because if x is out of this range, a sufficient discharge capacity cannot be obtained in a wide temperature range. In the first invention, it is particularly preferable to use a hydrogen storage alloy having a composition in which x is in the range of 0.4 ≦ x ≦ 0.6. By using this hydrogen storage alloy in an alkaline storage battery, it is possible to obtain a sufficient discharge capacity in a wide temperature range and prolong the cycle life.

Further, in the second invention, LaNi _{3.6
Y in} Al _y Co _1.4-y needs to be set in the range of 0.2 ≦ y ≦ 0.8. This is because when a hydrogen storage alloy electrode containing a hydrogen storage alloy with y outside this range is used in an alkaline storage battery, similar to the case of the first invention, it does not show sufficient discharge capacity in a wide temperature range, and This is because the internal pressure of the storage battery becomes high and it becomes difficult to seal the storage battery. In the second invention, it is particularly preferable to use a hydrogen storage alloy having a composition in which y is in the range of 0.2 ≦ y ≦ 0.6. By using this hydrogen storage alloy in an alkaline storage battery, a sufficient discharge capacity can be obtained in a wide temperature range, the internal pressure of the storage battery is low, and the cycle life can be extended.

[0013]

The hydrogen storage alloy electrode of the first invention of the present invention is L
It is characterized by using a hydrogen storage alloy having a composition of aNi _4.0 Al _x Co _1.0-x (0.4 ≦ x ≦ 0.9). Further, the hydrogen storage alloy electrode of the second invention of the present invention is LaNi _3.6 Al _x Co _1.4-x (0.2 ≦ x ≦ 0.
It is characterized by using a hydrogen storage alloy having the composition of 8).

The hydrogen storage alloy used in the hydrogen storage alloy electrode of the present invention basically has a CaCu ₅ type structure,
La is used for the Ca site, and Ni and A are used for the Cu site.
1 and Co are used. In this hydrogen storage alloy, Al has the effect of lowering the plateau pressure, and when used in a storage battery, sufficient charging can be performed without increasing the internal pressure. This effect is sufficiently exhibited even at high temperatures, and the plateau pressure of hydrogen can be reduced even at high temperatures. Further, Al has an effect of forming an oxide film to prevent the inside of the alloy from being oxidized, thereby preventing the discharge capacity from decreasing.

In this hydrogen storage alloy alloy, C
o has the effect of lowering the overvoltage, and can prevent the discharge capacity from decreasing at low temperatures. In addition, Co has the effect of suppressing the volume expansion during hydrogen storage, and thus has the function of preventing the hydrogen storage alloy from becoming finely divided when charging is repeated and extending the life of the hydrogen storage alloy. Furthermore, Co has an effect of acting as a catalyst when oxygen gas is reduced by hydrogen gas, and reduces O ₂ gas generated during overcharge,
It has the effect of reducing the internal pressure at the end of charging of the sealed battery.

[0016] When adding Al and Co in LaNi _5, since lowering the discharge capacity excessively added in LaNi _5, it is necessary to optimize the amount of both. That is, LaNi _4.0 Al _x Co _1.0-x (0.4 ≦ x ≦
0.9) or LaNi _3.6 Al _x Co _1.4-x (0.2
It is necessary to set the composition so as to satisfy ≦ x ≦ 0.8). By setting the composition in this way, it is possible to obtain a hydrogen storage alloy electrode having a wide operating temperature range in which a high discharge capacity can be maintained. This hydrogen storage alloy electrode is
It can be used for alkaline storage batteries mounted in electric vehicles and the like. In addition, LaNi _4.0 Al _x Co _1.0-x
(0.4 ≦ x ≦ 0.6) or LaNi _3.6 Al _x Co
LaNi ₅ to be _1.4-x (0.2 ≦ x ≦ 0.6)
By adding Al and Co to the alloy, it is possible to extend the cycle life while maintaining a wide operating temperature range. In particular, LaNi _3.6 Al _x Co _1.4-x (0.2 ≦ x
In the composition of ≦ 0.6), the internal pressure of the storage battery can be lowered.

Here, in the hydrogen storage alloy of the present invention,
The reason for using La for the Ca site and Ni, Al, and Co for the Cu site is as follows. When Ti or Zr is added to the Ca site, a stable metal oxide film is formed on the surface of the hydrogen storage alloy. For this reason, the overvoltage of the hydrogen storage alloy electrode is increased, and the discharge characteristics at low temperature are significantly deteriorated. Further, the plateau pressure rises and the hydrogen storage amount remarkably decreases.

When Mn is added to the Cu site, the hydrogen storage alloy is pulverized due to repeated charging and discharging, the hydrogen storage alloy is dropped from the electrode, the life of the charging and discharging cycle is shortened, and Mn itself is reduced. Elutes in the electrolyte. Therefore, the life of the charge / discharge cycle is shortened.

When Fe is added to the Cu site, the hydrogen storage amount is significantly reduced. When Sn is added to the Cu site, the plateau pressure decreases, but the hydride is stabilized by that amount, and the discharge capacity of the hydrogen storage electrode decreases.

When Si is added to the Cu site, a stable metal oxide film is formed on the surface of the hydrogen storage alloy. For this reason, the overvoltage of the hydrogen storage alloy electrode is increased, and the discharge characteristics at low temperature are significantly deteriorated. In addition, the hydrogen storage amount of the hydrogen storage alloy also decreases.

When Zn is added to the Cu site, the difference in boiling point from other elements such as Ni is so large that it becomes difficult to manufacture it by the melting method. That is, the composition of the hydrogen storage alloy cannot be adjusted accurately.

[0022]

EXAMPLES Examples of the present invention will be specifically described below. (Example 1) First, a hydrogen storage alloy having a composition of LaNi _4.0 Al _0.4 Co _0.6 was prepared by arc melting. This hydrogen storage alloy was crushed in an argon gas atmosphere to produce an alloy powder of 100 mesh or less. Next, 5% by weight of Teflon particles as a binder was mixed with this alloy powder and kneaded sufficiently to obtain a kneaded product. The kneaded product was molded at room temperature under a pressure of 7.5 t / cm ² to prepare pellets having an outer diameter of 13 mm. Then, this pellet was pressure-bonded to a 100-mesh Ni current collector having a size of 20 mm × 20 mm at room temperature to produce a hydrogen storage alloy electrode. The weight of the hydrogen storage alloy contained in this electrode was 200 mg.

Here, the relationship between the hydrogen dissociation ratio and the pressure of the hydrogen storage alloy having the composition of LaNi _4.0 Al _0.4 Co _0.6 was investigated. The hydrogen dissociation ratio at each pressure was measured by a Sibelts type device. The results are shown in FIG. 1 and FIG.
Is shown in the graph. It can be seen from FIGS. 1 and 2 that the plateau pressure, that is, the pressure in the plateau region 10 of the graph is low regardless of whether the temperature is 30 ° C. or 60 ° C.

Next, a capacity of 600 is provided on the hydrogen storage alloy electrode, which is the negative electrode, through a separator made of polypropylene.
A nickel oxide electrode, which is a positive electrode of mAh, is wound, and this is inserted into an open acrylic container having an inner diameter of 100 mm and a height of 100 mm, and 5N-KOH is used as an electrolytic solution in the container.
Was injected and sealed to produce a storage battery. The capacity of this storage battery was about 50 mAh under the negative electrode regulation.

Using the battery thus manufactured, the discharge capacity of this hydrogen storage alloy electrode at each temperature was examined. The results are shown in the graph of FIG. Note that the discharge capacity was 10 per 1 g of the electrode alloy using a battery charging / discharging device.
The measurement was performed by charging the battery at a current density of 0 mA for 3 hours, allowing the battery to stand for 30 minutes after charging, and then discharging the battery at the same current density until the battery voltage became 1V. (Examples 2 to 6) As a hydrogen storage alloy, LaNi _4.0 A
l _0.5 Co _0.5 (Example 2), LaNi _4.0 Al _0.6 C
o _0.4 (Example 3), LaNi _4.0 Al _0.7 Co _0.3
(Example 4), LaNi _4.0 Al _0.8 Co _0.2 (Example 5), and LaNi _4.0 Al _0.9 Co _0.1 (Example 6) were used in the same manner as in Example 1 except that hydrogen storage alloys having the respective compositions were used. A hydrogen storage alloy electrode was produced.

The discharge capacity of this hydrogen storage alloy electrode at each temperature was examined in the same manner as in Example 1. The result is shown in Figure 3.
Is also shown in the graph. (Comparative Examples 1-5) As a hydrogen storage alloy, LaNi _4.0 C
o _1.0 (Comparative Example 1), LaNi _4.0 Al _0.1 Co _0.9
A hydrogen storage alloy having a composition of (Comparative Example 2), LaNi _4.0 Al _0.2 Co _0.8 (Comparative Example 3), LaNi _4.0 Al _0.3 Co _0.7 (Comparative Example 4), and LaNi _3.0 Co _1.8 Al _0.2 (Comparative Example 5) was used. A hydrogen storage alloy electrode was produced in the same manner as in Example 1 except that each was used.

The discharge capacity at each temperature of this hydrogen storage alloy electrode was examined in the same manner as in Example 1. The results are shown in the graph of FIG. 4 together with the results of the hydrogen storage alloy electrode of the first invention of the present invention.

As is apparent from FIG. 3, the hydrogen-absorbing alloy electrodes (Examples 1 to 6) of the first invention of the present invention are -20 ° C.
Sufficient discharge capacity (180mAh / g)
) Was able to be obtained.

On the other hand, as is clear from FIG.
Each of the hydrogen storage alloy electrodes (Comparative Examples 1 to 5) using the hydrogen storage alloy having a composition outside the scope of the first invention of the present invention is 7
The discharge capacity was very small in the high temperature range of 0 ° C, and it could not be used as a storage battery. Example 7 As a hydrogen storage alloy, LaNi _4.0 Al
_0.4 Co _0.6 (Example 1), LaNi _4.0 Al _0.5 Co
_0.5 (Example 2), and LaNi _4.0 Al _0.6 Co
_A hydrogen storage alloy electrode was produced in the same manner as in Example 1 using the hydrogen storage alloy having the composition of _0.4 (Example 3). This hydrogen storage alloy electrode was subjected to a cycle test at 20 ° C. The result is shown in the graph of FIG. The conditions for measuring the discharge capacity in this case were the same as in Example 1. (Comparative Example 6) As a hydrogen storage alloy, LaNi _4.0 Al
Example 1 using a hydrogen storage alloy having the composition _0.2 Co _0.8 and LaNi _4.0 Al _0.7 Co _0.3 (Example 4).
A hydrogen storage alloy electrode was produced in the same manner as in. This hydrogen storage alloy electrode was subjected to a cycle test at 20 ° C. The results are also shown in the graph of FIG. The conditions for measuring the discharge capacity in this case were the same as in Example 1.

As is clear from FIG. 5, the hydrogen storage alloy electrodes (Examples 1 to 3) of the first invention of the present invention are 100%.
Despite the repeated discharge of No. 3, a sufficient discharge capacity was shown even after the completion of 300 cycles. On the other hand, a hydrogen storage alloy electrode (Comparative Example 6) using a hydrogen storage alloy having a composition outside the scope of the first invention of the present invention and LaNi _4.0 Al
_The hydrogen storage alloy electrode (Example 4) using a hydrogen storage alloy having a composition of _0.7 Co _0.3 had a lower discharge capacity from around 60 cycles, and a considerably lower discharge capacity after 300 cycles. However, the hydrogen storage alloy electrode of Example 4 can obtain a sufficient discharge capacity in a wide temperature range. (Example 8) First, to produce a hydrogen-absorbing alloy having a composition of LaNi _3.6 Al _0.4 Co _1.0 with arc melting. This hydrogen storage alloy was crushed in an argon gas atmosphere to produce an alloy powder of 100 mesh or less. Next, 5% by weight of Teflon particles as a binder was mixed with this alloy powder and kneaded sufficiently to obtain a kneaded product. The kneaded product was molded at room temperature under a pressure of 7.5 t / cm ² to prepare pellets having an outer diameter of 13 mm. Then, this pellet was pressure-bonded to a 100-mesh Ni current collector having a size of 20 mm × 20 mm at room temperature to produce a hydrogen storage alloy electrode. The weight of the hydrogen storage alloy contained in this electrode was 200 mg.

Here, the relationship between the hydrogen dissociation ratio and the pressure of the hydrogen storage alloy having the composition of LaNi _3.6 Al _0.4 Co _1.0 was investigated. The hydrogen dissociation ratio at each pressure was measured by a Sibelts type device. The result is shown in the graph of FIG. It can be seen from FIG. 6 that the plateau pressure, that is, the pressure in the plateau region 20 of the graph, is low.

Next, a capacity of 600 is provided on the hydrogen storage alloy electrode, which is the negative electrode, through a separator made of polypropylene.
A nickel oxide electrode, which is a positive electrode of mAh, is wound, and this is inserted into an open acrylic container having an inner diameter of 100 mm and a height of 100 mm, and 5N-KOH is used as an electrolytic solution in the container.
Was injected and sealed to produce a storage battery. The capacity of this storage battery was about 50 mAh under the negative electrode regulation.

Using the storage battery thus manufactured,
The discharge capacity at each temperature of this hydrogen storage alloy electrode was investigated. The result is shown in the graph of FIG. Note that the discharge capacity was 10 per 1 g of the electrode alloy using a battery charging / discharging device.
The measurement was performed by charging the battery at a current density of 0 mA for 3 hours, allowing the battery to stand for 30 minutes after charging, and then discharging the battery at the same current density until the battery voltage became 1V.

A conductive material, a fluororesin, and an aqueous CMC solution are mixed with the hydrogen storage alloy to form a paste, and the paste mixture is applied to a nickel porous sheet and dried to form a negative electrode (about 4.4 Ah). Was produced. This negative electrode and a known nickel electrode are alternately laminated to form a positive electrode regulation (positive electrode capacity 6
0 Ah, negative electrode capacity 120 Ah) sealed battery (nominal capacity 6
0Ah) was prepared and its internal pressure characteristics were evaluated. Temperature 25
At ℃, charging is 1 / 5C-4hr, 1 / 10C-3hr, 1
The internal pressure was measured at three stages of / 20C-4 hr by incorporating a pressure sensor in the battery. Table 1 shows the measured values of the maximum internal pressure.

[0035]

[Table 1] (Examples 9 to 12) As a hydrogen storage alloy, LaNi _3.6
Al _0.2 Co _1.2 (Example 9), LaNi _3.6 Al _0.45
Co _0.95 (Example 10), LaNi _3.6 Al _0.6 Co
_0.8 (Example 11), and LaNi _3.6 Al _0.8 Co
_A hydrogen storage alloy electrode was produced in the same manner as in Example 8 except that each hydrogen storage alloy having the composition of _0.6 (Example 12) was used.

The discharge capacities of these hydrogen storage alloy electrodes at each temperature were examined in the same manner as in Example 8, and the results are also shown in the graph of FIG. Further, the internal pressure of the storage battery of these hydrogen storage alloy electrodes was examined in the same manner as in Example 8, and the results are also shown in Table 1. (Comparative Examples 7 to 10) As a hydrogen storage alloy, LaNi _3.6
Co _1.4 (Comparative Example 7), LaNi _3.6 Al _1.0 Co _0.4
(Comparative Example _{8), LaNi 3.6 Al 1.2 Co} 0.2 ( Comparative Example 9), and LaNi _3.6 Al _1.4 hydrogen except for using each of the hydrogen storage alloy having a composition of (Comparative Example 10) In the same manner as in Example 8 occlusion An alloy electrode was produced.

The discharge capacities of these hydrogen storage alloy electrodes at each temperature were examined in the same manner as in Example 8, and the results are shown in the graph of FIG. Further, the internal pressure of the storage battery of these hydrogen storage alloy electrodes was examined in the same manner as in Example 8, and the results are also shown in Table 1.

As is apparent from FIG. 7, the hydrogen storage alloy electrode of the second invention of the present invention is LaNi _3.6 Al _0.2 Co.
_1.2 (Example 9) -20 to 60 ° C, LaNi _3.6
Al _0.4 Co _1.0 (Example 8) and LaNi _3.6 Al
_{In the case of 0.45} Co _0.95 (Example 10), -20 to 70 ° C, L
aNi _3.6 Al _0.6 Co _0.8 (Example 11) and La
In the case of Ni _3.6 Al _0.8 Co _0.6 (Example 12) -10
Sufficient discharge capacity (180mAh / g)
) Was able to be obtained. Further, as can be seen from Table 1, the internal pressure of the storage battery was low in all cases.

On the other hand, as is clear from FIG.
The hydrogen storage alloy electrodes (Comparative Examples 7 to 10) using the hydrogen storage alloy having a composition outside the scope of the second invention of the present invention have low discharge capacities or very low discharge capacities at high temperatures. , It could not be used as a storage battery. Further, as can be seen from Table 1, it is difficult to simultaneously satisfy all of the temperature characteristics, the life characteristics, and the storage battery internal pressure characteristics unless the amounts of Al and Co are optimized. (Example 13) the hydrogen storage alloy, LaNi _3.6 Al
_0.4 Co _1.0 (Example 8), LaNi _3.6 Al _0.2 Co
_1.2 (Example _{9), LaNi 3.6 Al 0.45 Co} 0.95 ( Example 10), and LaNi _3.6 Al _0.6 Co _0.8 hydrogen in the same manner as in Example 8 using a hydrogen storage alloy having a composition of (Example 11) adsorption An alloy electrode was produced. This hydrogen storage alloy electrode was subjected to a cycle test at 20 ° C. The result is shown in the graph of FIG. The conditions for measuring the discharge capacity in this case were the same as in Example 8.

As a hydrogen storage alloy, LaNi _3.6 Al
_1.0 Co _0.4 (Comparative Example 8) and LaNi _3.6 Al _0.8
A hydrogen storage alloy electrode was produced in the same manner as in Example 8 using a hydrogen storage alloy having a composition of Co _0.6 (Example 12). This hydrogen storage alloy electrode was subjected to a cycle test at 20 ° C. The results are also shown in the graph of FIG. The conditions for measuring the discharge capacity in this case were the same as in Example 8.

As is clear from FIG. 9, the hydrogen-absorbing alloy electrodes (Examples 15 to 18) of the second invention of the present invention are 10
Despite repeating 0% discharge, a sufficient discharge capacity was shown even after the completion of 300 cycles. On the other hand, L
ANI _3.6 Al _1.0 hydrogen absorbing alloy electrode using a hydrogen storage alloy having a composition of Co _0.4 (Comparative Example 8) is significantly discharge capacity was decreased by 50 cycles. In addition, LaNi _3.6
In the hydrogen storage alloy electrode (Example 12) using the hydrogen storage alloy having the composition of Al _0.8 Co _0.6, the discharge capacity gradually decreased as the number of cycles increased.
After the end of 0 cycle, the discharge capacity was insufficient. However, the hydrogen storage alloy electrode of Example 12 can obtain a sufficient discharge capacity in a wide temperature range.

[0042]

As described above, the hydrogen storage alloy electrode of the present invention regulates the amounts of Al and Co contained in the LaNi alloy, that is, in the composition of LaNi _4.0 Al _x Co _1-x , 0.4 ≦ x ≦ 0.9, or 0.2 in the composition of LaNi _3.6 Al _x Co _1.4-x
Since ≦ x ≦ 0.8 is set, when used in an alkaline storage battery, it can be sufficiently charged, a sufficient discharge capacity can be obtained in a wide temperature range, and the storage battery can be sealed. It can be done easily. Also, LaNi _4.0
By setting 0.4 ≦ x ≦ 0.6 in the composition of Al _x Co _1-x , or by setting 0.2 ≦ x ≦ 0.6 in the composition of LaNi _3.6 Al _x Co _1.4-x , In addition to the above effects, the cycle life can be extended. Furthermore, since it is possible to prevent the internal pressure from rising during overcharging, it has become possible to reduce the weight of the battery by minimizing the strengthening of the battery and the battery case accompanying the sealing.

[Brief description of drawings]

FIG. 1 is a graph showing the plateau pressure at 30 ° C. of the hydrogen storage alloy used in the hydrogen storage alloy electrode of the first invention of the present invention.

FIG. 2 is a graph showing a plateau pressure at 60 ° C. of the hydrogen storage alloy used in the hydrogen storage alloy electrode of the first invention of the present invention.

FIG. 3 is a graph showing the relationship between discharge capacity and temperature for the hydrogen storage alloys of the first invention of various compositions of the present invention.

FIG. 4 is a graph showing the relationship between discharge capacity and temperature for the hydrogen storage alloys of the first invention of the present invention and comparative examples of various compositions.

FIG. 5 is a graph showing the relationship between discharge capacity and cycle life for the hydrogen storage alloy of the first invention of the present invention.

FIG. 6 is a graph showing the plateau pressure of the hydrogen storage alloy used in the hydrogen storage alloy electrode of the second invention of the present invention.

FIG. 7 is a graph showing the relationship between discharge capacity and temperature for the hydrogen storage alloys of the second invention of various compositions of the present invention.

FIG. 8 is a graph showing the relationship between discharge capacity and temperature for hydrogen storage alloys of comparative examples having various compositions.

FIG. 9 is a graph showing the relationship between discharge capacity and cycle life for the hydrogen storage alloy of the second invention of the present invention.

FIG. 10: Hydrogen storage alloy containing Mm (MmNi _4.0 Al
₄ is a graph showing the relationship between pressure and atomic ratio for _0.4 Co _0.6 ).

FIG. 11: Hydrogen storage alloy containing Mm (MmNi _3.6 Al
Graph showing the relationship between pressure and atomic ratio for _0.4 Co _1.0 ).

[Explanation of symbols]

 10, 20 ... Plateau area.

 ─────────────────────────────────────────────────── --- Continuation of the front page (72) Inventor Yoshie Wakiya 7-2 Nakayama, Aoba-ku, Sendai-shi, Miyagi 7-2, Tohoku Electric Power Co., Inc.

Claims (4)

[Claims] 1. In an electrode using a hydrogen storage alloy as an active material, the hydrogen storage alloy is LaNi _4.0 Al _x Co _1.0-x.
A hydrogen storage alloy electrode having a composition of (0.4 ≦ x ≦ 0.9). 2. An electrode using a hydrogen storage alloy as an active material, wherein the hydrogen storage alloy is LaNi _4.0 Al _x Co _1.0-x.
A hydrogen storage alloy electrode having a composition of (0.4 ≦ x ≦ 0.6). 3. An electrode using a hydrogen storage alloy as an active material, wherein the hydrogen storage alloy is LaNi _3.6 Al _y Co _1.4-y.
A hydrogen storage alloy electrode having a composition of (0.2 ≦ y ≦ 0.8). 4. A electrode using hydrogen-absorbing alloy as an active material, the hydrogen storage alloy LaNi _3.6 Al _y Co _1.4-y
A hydrogen storage alloy electrode having a composition of (0.2 ≦ y ≦ 0.6).