JP3432976B2 - Hydrogen storage alloy electrodes for metal-hydride alkaline storage batteries - 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-absorbing alloy electrode for a metal-hydride alkaline storage battery, and more particularly to a metal-metal alloy excellent in both high rate discharge characteristics and charge / discharge cycle characteristics in the initial charge / discharge cycle. The present invention relates to an improvement of a hydrogen storage alloy, which is a hydrogen storage material, for the purpose of providing a hydrogen storage alloy electrode that makes it possible to obtain a hydride alkaline storage battery.

[0002]

2. Description of the Related Art In recent years,
A metal / hydride alkaline storage battery that uses a metal compound such as nickel hydroxide for the positive electrode and a new material hydrogen storage alloy for the negative electrode has a high energy density per unit weight and unit volume and is capable of high capacity. Therefore, it is attracting attention as a next-generation alkaline storage battery that replaces the nickel-cadmium storage battery.

As a hydrogen storage alloy for a metal / hydride alkaline storage battery, one obtained by pulverizing a molten alloy in a mold after water-cooling solidification is generally used (hereinafter, this hydrogen storage alloy will be referred to as "hydrogen storage alloy"). Referred to as "normally coagulated product").

However, since a solidified product usually has a large amount of segregation (deviation of concentration of component elements), alloy particles are cracked when hydrogen is occluded or released during charging / discharging, and the specific surface area is apt to increase. . Therefore, a metal / hydride alkaline storage battery that uses a solidified product as a negative electrode material is excellent in high rate discharge characteristics at the beginning of the charge / discharge cycle, but the segregated portion easily becomes a starting point of oxidative deterioration (corrosion). It has a problem that the life is generally short.

As a method for improving the cycle life, it has been previously proposed to use a solidified product that has been subjected to an annealing treatment (a treatment of heating and holding at a predetermined temperature for a predetermined time) (Japanese Patent Laid-Open No. 60-60). 89066).

However, when the solidified product is usually annealed, segregation is reduced, so that the cycle life is longer than that of the untreated product. On the other hand, the segregation is reduced and the size of the crystal grains is increased. Since (the sum of the thicknesses of two adjacent layers in a layered structure in which a layer having a high concentration of rare earth elements and a layer having a low concentration of rare earth elements alternately appear) becomes too large, cracks are less likely to occur in the particles, and The high rate discharge characteristics in the initial stage of the discharge cycle are remarkably deteriorated as compared with the untreated one.

In view of the above-described difficult problems to solve in a normally solidified product, recently, a hydrogen storage alloy produced by a so-called single roll method in which a molten alloy is jetted to the peripheral surface of a roll rotating at high speed to rapidly solidify is a metal. Proposed as a negative electrode material for hydride alkaline storage batteries (Japanese Patent Laid-Open No. 6-187)
979, etc.).

Since the hydrogen storage alloy produced by this single roll method is obtained by quenching and solidifying the molten alloy,
When the molten alloy is solidified, it is less affected by the gravitational field, and segregation is less than that of a normally solidified product.

However, the hydrogen storage alloy produced by the single roll method has nonuniform crystal grain sizes. That is, as the charging / discharging cycle progresses, there are a fragile portion (on the open surface side where the crystal grain size is large) and a fragile portion (on the roll surface side where the crystal grain size is small).

Further, in JP-A-63-291363, a flaky hydrogen storage alloy having a thickness of 40 μm or less in which crystal grains are oriented in a constant crystal plane (probably (hk0) plane) is pulverized. It has been shown that it is preferable to use one as an electrode material. However, in this hydrogen storage alloy, there is a problem that the electrocatalytic ability is not good because the selectively oriented surface appears on the surface of the alloy particles. In addition, thickness 40
When a thin piece having a thickness of μm or less is used, the contact resistance between the alloy particles is large because the alloy particles after pulverization are fine. Therefore, there is a problem that the utilization rate of the hydrogen storage alloy is low and the cycle life is short.

FIG. 2 is an enlarged cross-sectional view schematically showing the appearance of crystal grains appearing in the cross section of the hydrogen storage alloy B produced by the single roll method when cut along the strip length direction along a plane perpendicular to the strip surface. It is a figure (only a part is drawn). In the figure, the white portion 21 is a layer having a high concentration of rare earth elements, and the black portion 22 is a layer having a low concentration thereof, and the sum of the thicknesses of these two adjacent layers indicates the size of the crystal grain. 25 is the thickness of the ribbon. As shown in FIG. 2, the crystal grain size 23 on the open surface side O is large and the crystal grain size 24 on the roll surface side R is small. The open surface side O having a large crystal grain size 23 is easily cracked and activated, while the roll surface side R having a small crystal grain size 24 is hard to crack and activated. As a result, the charge / discharge depth on the open surface side O, which is easily activated, becomes deep, and therefore the hydrogen storage alloy B is easily pulverized when charge / discharge is repeated.

[0012] As described above, the hydrogen storage alloy produced by the single roll method has a short cycle life because it is easily pulverized when charging and discharging are repeated, and there has been a strong demand for its improvement.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a metal-hydride alkali excellent in both high rate discharge characteristics and charge / discharge cycle characteristics at the beginning of charge / discharge cycles. It is an object to provide a hydrogen storage alloy electrode that makes it possible to obtain a storage battery.

[0014]

A hydrogen storage alloy electrode for a metal-hydride alkaline storage battery according to the present invention (hereinafter, referred to as "the electrode of the present invention") for achieving the above object is provided.
An average prepared by the single roll method, in which the minimum crystal grain size defined below on the roll surface side is 0.2 μm or more and the maximum crystal grain size defined below on the open surface side is 20 μm or less. Thickness 0.08 to 0.35 mm (however, 0.
08mm or more, general except to the extent of less than 0.23mm)
Formula: MmR _x (Mm is misch metal; R is Ni, C
o, Al and Mn; x is 4.4 to 5.2)
The alloy powder obtained by crushing the ribbon-shaped rare earth / nickel-based hydrogen storage alloy is used as a hydrogen storage material.

Grain size: The level of rare earth elements in the alloy
It is the sum of the thicknesses of these two layers in a multi-layer structure in which a layer having a higher concentration of rare earth elements and a layer having a lower concentration of the same appear alternately as compared with the uniform concentration .

The thickness (average thickness) of the ribbon of the rare earth / nickel hydrogen storage alloy in the present invention is 0.08 to 0.35.
mm (However, the range of 0.08 mm or more and less than 0.23 mm
Are excluded) . If the average thickness exceeds 0.35 mm, the crystal grain size in the thickness direction of the ribbon becomes non-uniform, which shortens the cycle life. On the other hand, if an average thickness of less than 0.08 mm is used,
Since the particle surface of the alloy is oriented to the (hk0) plane and the electrode catalytic activity is reduced, the high rate discharge characteristics are deteriorated, and the particle size of the alloy particles forming the electrode is small, so The contact resistance of is increased. As a result, the utilization efficiency of the hydrogen storage alloy powder is reduced, and the cycle life is shortened.

In the rare earth / nickel-based hydrogen storage alloy according to the present invention, the minimum crystal grain size on the roll surface side is 0.2.
More than μm, the maximum size of crystal grains on the open side is 20 μm
It is as follows. If the minimum and maximum are out of the above range, the high rate discharge characteristics at the beginning of the charge / discharge cycle may deteriorate,
The cycle life is shortened. That is, 0.2μ
When crystal grains of less than m are mixed on the roll surface side, the hydrogen storage alloy is less likely to crack, which causes deterioration of high-rate discharge characteristics at the beginning of the charge / discharge cycle. On the other hand, when crystal grains having a size of more than 20 μm are mixed on the open surface side, the hydrogen storage alloy is pulverized and is easily oxidized and deteriorated, which shortens the cycle life.

Rare earth / nickel based hydrogen used in the present invention
The storage alloy has the general formula: MmR _x (Mm is mischmeta)
R is composed of Ni, Co, Al and Mn; x is 4.
Mm, Ni, Co, Al, and Mn represented by 4 to 5.2)
It is an alloy.

The preferable Co content of the Mm.Ni.Co.Al.Mn alloy is 0.4 Co per 1 mol part of Mm.
.About.0.9 parts by mole. In addition, the above Mm, Ni, Co,
A suitable Ni content of the Al.Mn alloy is 2.8 to 3.6 parts by mol of Ni with respect to 1 part by mol of Mm.

In the electrode of the present invention, for example, a ribbon-shaped rare earth / nickel-based hydrogen storage alloy is produced by rapidly solidifying molten alloy by a single roll method at a roll peripheral velocity of 50 to 1000 cm / sec in an inert gas or vacuum. Then, the ribbon-shaped rare earth / nickel-based hydrogen storage alloy is placed in an inert gas or in vacuum 62
Annealed at a temperature of 0 to 1000 ° C., the annealed ribbon-shaped rare earth / nickel-based hydrogen storage alloy is crushed to prepare an alloy powder, and the alloy powder and the binder solution are mixed to obtain It is prepared by coating or filling the electrode base material with the slurry. 50 alloy molten metal by single roll method
The average thickness of the thin strip is 0.08 to 0.35 mm ( however, by rapidly solidifying at a roll peripheral speed of up to 1000 cm / sec.
However, the range of 0.08 mm or more and less than 0.23 mm is excluded.
Can be continued), and by annealing at a temperature of 620-1,000 ° C, the crystal grain size minimum 0.2μm or more, it can be a maximum 20μm or less.

The average thickness of the ribbon of the rare earth / nickel based hydrogen storage alloy depends on the roll peripheral speed. When the roll peripheral speed is increased and the solidification speed is increased, the average thickness of the ribbon becomes smaller. On the other hand, the size of the crystal grain depends on the annealing temperature during the annealing treatment. Usually, when the annealing temperature is raised, the minimum of the crystal grain size increases, but the maximum hardly changes. That is, the variation in crystal grain size is reduced. However, when the annealing temperature exceeds 1000 ° C. and approaches the melting point of the alloy (about 1200 ° C.), the hydrogen storage alloy partially remelts at the crystal grain boundaries, becomes extremely hard to crack, and becomes inactive. The annealing time is about 1 to 10 hours.
Usually, the effect of annealing is saturated in about 10 hours.

[0022]

In the present invention, the rare earth / nickel-based hydrogen storage alloy has an average thickness of 0.08 to 0.35 mm (however, 0.
(Excluding the range of 08 mm or more and less than 0.23 mm) , the crystal grain size in the thickness direction of the ribbon is uniform.
Therefore, it is less likely to be pulverized in the charge / discharge cycle.
Further, since the lower limit of the average thickness is regulated, the selective orientation of the grain surface of the alloy to the (hk0) plane is not so large. Therefore, the electrode catalytic ability is high.

Furthermore, in the rare earth / nickel-based hydrogen storage alloy according to the present invention, there are no excessively small crystal grains on the roll surface side and no excessively large crystal grains on the open surface side. The alloy cracks moderately and does not become finely pulverized even after repeated charging and discharging.

Therefore, the metal-hydride alkaline storage battery using the electrode of the present invention as the negative electrode is excellent in both high rate discharge characteristics and charge / discharge cycle characteristics at the beginning of charge / discharge cycles.

[0025]

EXAMPLES The present invention will be described in more detail based on the following examples, but the invention is not intended to be limited to the following examples, and various modifications may be made without departing from the scope of the invention. Is possible.

( Examples 1 to 9 and Reference Examples 1 to 4 ) [Preparation of Hydrogen Storage Alloy] Alloy component metals (all having a purity of 99.9% or more) are weighed and mixed, and the mixture is heated in a high-frequency melting furnace under vacuum. After being melted in, the various cooling rates shown in Table 1 (roll peripheral speed: 50, 100, 300, 5 by the single roll method (roll diameter: 350 mm))
00 or 1000 cm / sec), and the composition formula: Mm
A ribbon-shaped rare earth / nickel-based hydrogen storage alloy represented by Ni _3.4 Co _0.8 Al _0.3 Mn _0.5 (band length: about 30 to 10
0 mm; band width: about 20 to 50 mm) was produced. The thickness of these ribbons was arbitrarily selected and measured at 10 locations, and the average value was used as the thickness of the ribbons. Table 1 shows the thickness (average thickness) of each ribbon.

Next, these rare earth / nickel-based hydrogen storage alloys were subjected to various temperatures (620, 700, 8) shown in Table 1.
Annealing treatment was performed in Ar gas at 00, 900, 1000 or 1200 ° C. for 6 hours.

Each of these annealed rare earth / nickel-based hydrogen storage alloys was cut perpendicularly to the band surface along the band length direction, and the backscattered electron image of the cross section was taken by a scanning electron microscope (manufactured by JEOL Ltd.). No. “JEOL866”), and the maximum crystal grain size on the open surface side and the minimum crystal grain size on the roll surface side were determined. Both the maximum and minimum are average values for 10 samples of each rare earth / nickel-based hydrogen storage alloy. Table 1 shows the maximum and minimum crystal grain sizes of the rare earth / nickel-based hydrogen storage alloys.

FIG. 1 is a schematic view showing a state of crystal grains appearing in a cross section of an annealing-processed ribbon-shaped hydrogen storage alloy A (only a part is depicted). In the figure, a white portion 1 is a layer having a high rare earth element and cobalt concentration and a low manganese concentration, and a black portion 2 is a layer having a low rare earth element and cobalt concentration and a high manganese concentration. 3 indicates the size of crystal grains on the open surface side O, and 4 indicates the size of crystal grains on the roll surface side R. 5
Indicates the thickness of the ribbon. As shown in FIG. 1, the size of the crystal grains 4 on the roll surface side R becomes large due to the annealing treatment, and as a result, the difference from the size 3 of the crystal grains on the open surface side O becomes small and the thickness of the ribbon becomes small. The size of the crystal grains in the direction is more uniform than that of the hydrogen storage alloy B (see FIG. 2) before the annealing treatment.

[Preparation of Hydrogen Storage Alloy Electrode] Each of the annealed rare earth / nickel based hydrogen storage alloys is mechanically crushed in an inert gas (Ar gas) atmosphere into a powder having an average particle size of about 70 μm, and sieved. Then, the particle size was adjusted to 100 mesh under (the maximum particle size was adjusted to the same value in all of the following Examples and Comparative Examples). Then, 90 parts by weight of this powder was mixed with 10 parts by weight of a 2.5% by weight aqueous solution of polyethylene oxide to prepare a slurry.

Next, this slurry was applied to a punching metal made by plating nickel with iron and dried to prepare hydrogen storage alloy electrodes E1 to E13.

[Preparation of Nickel Hydride Alkaline Storage Battery] AA was sequentially prepared by using the above hydrogen storage alloy electrodes as negative electrodes.
Size (AA type) positive electrode dominant nickel-hydride alkaline storage battery (battery capacity: 1200 mAh ± 10 mA
h) A1 to A13 were produced. A conventionally known sintered nickel electrode is used as the positive electrode, a polyamide non-woven fabric is used as the separator, and 30% by weight is used as the alkaline electrolyte.
Aqueous potassium hydroxide solution was used respectively.

[0033]

[Table 1]

[0034] (Comparative Example 1) except for using a conventional coagulation method instead of the single roll method real
In the same manner as in Examples 1 to 9 , massive rare earth / nickel based hydrogen storage alloys having the same composition were produced.

Then, this alloy was annealed at 900 ° C. for 6 hours (the annealing time was also unified to 6 hours in the following Examples or Comparative Examples), mechanically crushed and sieved. The maximum grain size is 35μ
m, and the minimum powder was 10 μm. The maximum and minimum crystal grain sizes were obtained by measuring the spacing between adjacent white line portions observed in a backscattered electron beam image in the direction perpendicular to the white line (also regarding the maximum and minimum crystal grain sizes below. Obtained in the same manner.).

Comparative electrode CE1 and battery B1 were prepared in the same manner as in Examples 1 to 9 except that this powder was used as the hydrogen storage material.

(Comparative Example 2) A roll peripheral velocity was set to 10 cm / sec, and an annealing temperature was set to 90.
In the same manner as in Examples 1 to 9 except that the temperature was 0 ° C., the average thickness was 0.57 mm, the maximum crystal grain size on the open side was 40 μm, and the minimum crystal grain size on the roll side was 0.
A 2 μm powder was made.

Comparative electrode CE2 and battery B2 were prepared in the same manner as in Examples 1 to 9 except that this powder was used as the hydrogen storage material.

(Comparative Example 3) The roll peripheral velocity was 300 cm / sec, and the annealing temperature was 5
In the same manner as in Examples 1 to 9 except that the temperature was set to 00 ° C,
A powder having an average thickness of 0.23 mm, a maximum crystal grain size on the open surface side of 15 μm, and a minimum crystal grain size on the roll surface side of 0.01 μm or less was prepared.

Comparative electrode CE3 and battery B3 were produced in the same manner as in Examples 1 to 9 except that this powder was used as the hydrogen storage material.

(Comparative Example 4) The roll peripheral velocity was 300 cm / sec, and the annealing temperature was 1.
Similar to Examples 1 to 9 except that the temperature was 200 ° C., the average thickness was 0.23 mm, the maximum crystal grain size on the open surface side was 25 μm, and the minimum crystal grain size on the roll surface side was A 0.4 μm powder was prepared.

Comparative electrode CE4 and battery B4 were produced in the same manner as in Examples 1 to 9 except that this powder was used as the hydrogen storage material.

(Comparative Example 5) An example except that a normal solidification method (water cooling solidification method) was used in place of the single roll method and no annealing treatment was carried out.
As in 1 to 9 , the maximum crystal grain size is 25μ.
m, and the minimum powder was 7 μm.

Comparative electrode CE5 and battery B5 were produced in the same manner as in Examples 1 to 9 except that this powder was used as the hydrogen storage material.

(Comparative Example 6) An average thickness of 0.23 mm and a size of crystal grains on the open surface side were obtained in the same manner as in Examples 1 to 9 except that the roll peripheral speed was 300 cm / sec and no annealing treatment was performed. Maximum of 10
μm, the minimum crystal grain size on the roll side is 0.01μ
A powder of m or less was produced.

Comparative electrode CE6 and battery B6 were produced in the same manner as in Examples 1 to 9 except that this powder was used as the hydrogen storage material.

[0047] (Comparative Example 7) molten alloy having the same composition as in Example 1 to 9 (MmNi _3.4 Co
_{After 0.8} Al _0.3 Mn _0.5 ) was solidified by the atomization method, it was annealed at 900 ° C. for 6 hours to prepare a hydrogen storage alloy powder. The maximum and minimum crystal grain sizes were 8 μm and 0.1 μm, respectively.

Comparative electrode CE7 and battery B7 were produced in the same manner as in Examples 1 to 9 except that this powder was used as the hydrogen storage material.

Comparative Example 8 An average thickness of 0.06 mm and a crystal grain on the open surface side were obtained in the same manner as in Examples 1 to 9 except that the roll peripheral speed was 1500 cm / sec and the annealing temperature was 900 ° C. A powder having a maximum size of 5 μm and a minimum size of crystal grains on the roll surface side of 0.2 μm was prepared.

Comparative electrode CE8 and battery B8 were produced in the same manner as in Examples 1 to 9 except that this powder was used as the hydrogen storage material.

(Comparative Example 9) Roll peripheral speed was 3000 cm / sec (roll diameter: 150 m)
m) and the annealing temperature was 900 ° C.
In the same manner as in Examples 1 to 9 , a powder having an average thickness of 0.04 mm, a maximum crystal grain size on the open surface side of 2 μm, and a minimum crystal grain size on the roll surface side of 0.2 μm (average grain size). Diameter:
55 μm) was prepared. The roll peripheral speed is 3000
Since the speed was as high as cm / sec, a particle having an average particle size of 70 μm could not be obtained.

Comparative electrode CE9 and battery B9 were prepared in the same manner as in Examples 1 to 9 except that this powder was used as the hydrogen storage material.

(Comparative Example 10) Roll peripheral speed was 5000 cm / sec (roll diameter: 150 m)
m) and the annealing temperature was 900 ° C.
In the same manner as in Examples 1 to 9 , a powder having an average thickness of 0.03 mm, a maximum crystal grain size on the open surface side of 2 μm, and a minimum crystal grain size on the roll surface side of 0.15 μm (average grain size). Diameter: 48 μm) was produced. In addition, roll peripheral speed is 50
Since the speed was as high as 00 cm / sec, an average particle size of 70 μm could not be obtained.

Comparative electrode CE10 and battery B10 were produced in the same manner as in Examples 1 to 9 except that this powder was used as the hydrogen storage material.

Table 2 collectively shows the alloy preparation conditions, the average thickness of the prepared hydrogen storage alloy powders, and the maximum and minimum crystal grain sizes in Comparative Examples 1 to 10.

[0056]

[Table 2]

<High rate discharge capacity at the beginning of charge / discharge cycle> The batteries A1 to A13 and the batteries B1 to B10 were stored at room temperature (about 25
After charging for 16 hours at 120mA at 60 ° C
At 120 mA, it was discharged to 0.95 V for activation treatment.

Then, each battery was set to 1.1 at 1200 mA.
After charging for an hour, discharge to 0.95V at 4.8A,
The high rate discharge capacity was determined. The discharge capacity of each of the three batteries was measured, and the average thereof was defined as the high rate discharge capacity of each battery.
The results are shown in Table 1 or Table 2 above.

<Cycle Life> The batteries A1 to A13 and the batteries B1 to B10 were activated under the same conditions as above, and then charged at 1200 mA for 1.1 hours at room temperature,
After pausing for a period of time, a charge / discharge cycle test in which one cycle is a process of discharging at 1200 mA to 1.0 V was performed to examine the cycle life of each battery. The cycle life of each of the 10 batteries was determined, and the average of 8 batteries excluding the one having the shortest life and the one having the longest life was taken as the cycle life of each battery. The cycle life was determined as the number of cycles (times) until the battery capacity dropped to 960 mAh or less. The results are shown in Table 1 or Table 2 above.

The batteries A1 to A13 shown in Table 1 are excellent in high rate discharge characteristics at the beginning of the charge / discharge cycle and have a long life, whereas the batteries B1 to B10 shown in Table 2 are high at the beginning of the charge / discharge cycle. There are problems with inferior rate discharge characteristics, short cycle life, or both.

The batteries A1 to A13 are excellent in high rate discharge characteristics in the early stage of charge and discharge cycles and have a long life because the hydrogen storage alloy used for the negative electrode has little segregation of Mn and the like and has an excessively small or large crystal grain. Is considered to be due to the absence of.

Although the battery B1 has a long cycle life,
The high rate discharge capacity at the beginning of the charge / discharge cycle is small. this is,
It is considered that the hydrogen storage alloy became hard to crack because the distribution of Mn was made uniform to eliminate the segregation and the crystal grains became too large.

The battery B2 has a large high rate discharge capacity at the beginning of the charge / discharge cycle, but has a short cycle life. this is,
It is considered that the open surface side is easily cracked and activated, but the roll surface side is hard to be cracked and thus hard to be activated, so that the charge / discharge depth on the open surface side is deep and the hydrogen storage alloy is finely pulverized.

Battery B3 has a large high rate discharge capacity at the beginning of the charge / discharge cycle, but has a short cycle life. this is,
It is considered that there was a portion where activation was insufficient because the annealing temperature was too low, and the charge and discharge depth of the activated portion became deep, and the hydrogen storage alloy was pulverized.

Battery B4 has a small high rate discharge capacity at the beginning of the charge / discharge cycle and a short cycle life. The high rate discharge capacity at the beginning of the charge / discharge cycle is small because the annealing temperature was close to the melting point of the alloy, and the hydrogen storage alloy was partially redissolved at the crystal grain boundaries, making it very difficult to crack and difficult to activate. The reason why the cycle life is short is considered to be that the utilization efficiency of the hydrogen storage alloy is lowered due to the difficulty of activation.

Battery B5 has a large high rate discharge capacity at the beginning of the charge / discharge cycle, but has a short cycle life. The reason why the cycle life is short is that segregation of Mn is present in the hydrogen storage alloy because the crystal grains are large but are not annealed.

Battery B6 has a large high rate discharge capacity at the beginning of the charge / discharge cycle, but has a short cycle life. this is,
It is considered that the open surface side is easily cracked and activated, but the roll surface side is hard to be cracked and thus hard to be activated, so that the charge / discharge depth on the open surface side is deep and the hydrogen storage alloy is finely pulverized.

Battery B7 has a small high rate discharge capacity at the beginning of the charge / discharge cycle and a short cycle life. The cycle life is short because the atomized solidified product has a large variation in the particle size distribution, and therefore the size of the crystal grains varies depending on the particle size even after annealing, especially the activation of small particles of 30 μm is poor, and as a whole alloy particles It is thought that this is because the usage efficiency of is poor.

In Battery B8, since the roll surface side of the alloy particles has a strong selective orientation on the (hk0) plane, the minimum grain size on the roll surface side is increased to 0.2 μm by the annealing treatment. However, sufficient activation cannot be obtained. Therefore, the high rate discharge capacity is small. Further, in the battery B8, alloy powder having an average particle size of 70 μm is used, but the thickness of the ribbon is 0.06 mm (60 μm).
Since it is thin, there are many flat particles, and the contact resistance between alloy particles is large. Therefore, the utilization efficiency of the alloy particles as a whole is poor and the cycle life is short.

In the batteries B9 and B10, alloy powder obtained by crushing a thinner ribbon than the ribbon used in the battery B8 is used, so that the high-rate discharge capacity is smaller than that of the battery B8 and the cycle is longer. It has a short life.

<C of Mm / Ni / Co / Al / Mn alloy
Relationship between o content and cycle life> Co in alloy component metal
Example 8 (roll peripheral speed: 3 except that the amount was variously changed)
00 cm / sec; annealing temperature: 900 ° C.) and composition formula: MmNi _4.2-y Co _y Al _0.3 Mn _0.5 (y
= 0.3, 0.4, 0.5, 0.6, 0.7, 0.9 or 1.0), 7 kinds of hydrogen storage alloy powders represented by

Then, a hydrogen storage alloy electrode and a nickel-hydride alkaline storage battery were prepared in the same manner as in Example 8 except that these hydrogen storage alloy powders were used as the hydrogen storage material.

A high-rate discharge test and a charge-discharge cycle test were conducted on each of the prepared nickel-hydride alkaline storage batteries under the same conditions as above, and the high-rate discharge characteristics and the cycle life of each battery at the beginning of the charge-discharge cycle were examined. The results are shown in Table 3. In Table 3, the result of the battery A8 is also shown by being transferred from Table 1.

[0074]

[Table 3]

From Table 3, Mm, Ni, Co, Al and Mn
In the case of an alloy, in order to obtain a nickel-hydride alkaline storage battery that is excellent in both high rate discharge characteristics and charge / discharge cycle characteristics at the beginning of charge / discharge cycles, 0.4 to 0.9 mol of Co is added to 1 mol part of Mm. It can be seen that it is preferable to use those containing parts.

<Mm / Ni / Co / Al / Mn alloy N
Relationship between i content and cycle life> Ni in alloy component metal
Example 8 (roll peripheral speed: 3 except that the amount was variously changed)
00cm / sec; annealing temperature: 900 ° C) and the same way the composition _{formula: MmNi z Co 0.8 Al 0.3 Mn} 0.5 (z =
Three types of hydrogen storage alloy powders represented by 2.8, 3.2 or 3.6) were produced.

Then, a hydrogen storage alloy electrode and a nickel-hydride alkaline storage battery were prepared in the same manner as in Example 8 except that these hydrogen storage alloy powders were used as the hydrogen storage material.

A high rate discharge test and a charge / discharge cycle test were conducted on each of the prepared nickel-hydride alkaline storage batteries under the same conditions as above, and the high rate discharge characteristics and the cycle life of each battery at the initial stage of the charge / discharge cycle were examined. The results are shown in Table 4. In Table 4, the result of Battery A8 is also shown by being transferred from Table 1.

[0079]

[Table 4]

From Table 4, Mm, Ni, Co, Al, Mn
In the case of an alloy, in order to obtain a nickel-hydride alkaline storage battery that is excellent in both high rate discharge characteristics and charge / discharge cycle characteristics in the early stages of charge / discharge cycles, 2.8 to 3.6 mol of Ni relative to 1 mol part of Mm. It can be seen that it is preferable to use those containing parts.

[0081]

[0082]

The electrode of the present invention has less segregation,
Moreover, since a rare earth / nickel-based hydrogen storage alloy that does not contain excessively small crystal grains or excessively large crystal grains is used as the hydrogen storage material, by using the electrode of the present invention as the negative electrode, high rate discharge at the beginning of the charge / discharge cycle can be achieved. It is possible to obtain a metal-hydride alkaline storage battery excellent in both characteristics and charge / discharge cycle characteristics.

[Brief description of drawings]

FIG. 1 is a schematic view showing a state of crystal grains appearing in a cross section of a hydrogen storage alloy that is annealed after being rapidly solidified by a single roll method.

FIG. 2 is a schematic diagram showing a state of crystal grains appearing in a cross section of a hydrogen storage alloy that has not been annealed after being rapidly solidified by a single roll method.

[Explanation of symbols]

A Annealed ribbon-shaped hydrogen storage alloy 1 White area (layer with high concentration of rare earth elements and cobalt) 2 Black part (layer with low concentration of rare earth elements and cobalt) 3 Size of crystal grains on open side O 4 Size of crystal grain on roll side R 5 Thickness of ribbon

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasushi Kuroda 2-5-5 Keihan Hondori, Moriguchi City, Osaka Prefecture Sanyo Electric Co., Ltd. (72) Inventor Nobuyuki Higashiyama 2-5 Keihan Hondori, Moriguchi City, Osaka Prefecture 5 In Sanyo Electric Co., Ltd. (72) Koji Nishio 2-5-5 Keihan Hondori, Moriguchi City, Osaka Prefecture 5-5 Sanyo Electric Co., Ltd. (72) Toshihiko Saito 2-5 Keihan Hondori, Moriguchi City, Osaka Prefecture No. 5 within Sanyo Electric Co., Ltd. (56) Reference JP-A-7-268519 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01M 4/24-4/26 H01M 4 / 38

Claims (3)

(57) [Claims] 1. A single roll method in which the minimum size of crystal grains defined below on the roll side is 0.2 μm or more and the maximum size of crystal grains defined below on the open side is 20 μm or less. Average thickness of 0.08-0.35mm
(However, if the range is 0.08 mm or more and less than 0.23 mm,
Except) general formula: MmR _x (Mm is misch metal; R
Consists of Ni, Co, Al and Mn; x is 4.4 to
An alloy powder obtained by crushing a ribbon-shaped rare earth / nickel-based hydrogen storage alloy represented by 5.2) is used as a hydrogen storage material for a metal-hydride alkaline storage battery. Hydrogen storage alloy electrode. Grain size: Compared with the average concentration of rare earth elements in the alloy
It refers to the sum of the thicknesses of these two layers in a multilayer structure a high concentration layer of the same concentration of the rare earth element and a lower layer appear alternately Te. 2. The rare earth / nickel-based hydrogen storage alloy,
0.4 to 0.9 Co for 1 mol part of misch metal
The metal-hydride alkali according to claim 1, which comprises a molar part.
Hydrogen storage alloy electrode for storage battery. 3. The rare earth / nickel-based hydrogen storage alloy,
2.8-3.6 Ni for 1 mol part of misch metal
The metal-hydride alkali according to claim 1, which comprises a molar part.
Hydrogen storage alloy electrode for storage battery.