JPH0982322A - Hydrogen storage alloy electrode for metal-hydride alkaline storage battery and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the characteristics of a battery in the initial stage of charge/discharge cycles by crushing an alloy having the specified crystal grain size, the specified average thickness and composition, and using the obtained alloy powder as a hydrogen storage material. SOLUTION: The minimum crystal grain size on the roll surface side is made 0.2μm or more and the maximum crystal grain size on the open surface side is made 18μm or less. The alloy powder obtained by crushing a thin plate- shaped Mm.Ni.Co.Al.Mn alloy represented by general formula MmRx having an average thickness of 0.08-0.35mm produced by a single roll process is used as a hydrogen storage material. Mm represents misch metal, R represents Ni, Co, Mn, or Al, and x is 4.5-4.9. Since the excessive small crystal grains do not exist on the roll surface side and excessive large crystal grains do not exist on the open surface side, the alloy is appropriately broken in the initial stage of charge/discharge cycles, and in addition the generation of fine powder is prevented even if charge/discharge cycles are repeated. Since the total amount to molar part of the alloy is regulated, the alloy is easy to break.

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 electrode for a metal-hydride alkaline storage battery and a method for manufacturing the same, and more particularly, to a high rate discharge characteristic at the beginning of a charge / discharge cycle, a charge / discharge cycle characteristic and an overcurrent resistance. With the aim of providing a hydrogen storage alloy electrode that makes it possible to obtain a metal-hydride alkaline storage battery having excellent charging characteristics,
The present invention relates to improvement of a hydrogen storage alloy that is a hydrogen storage material.

[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)
No. 979).

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. Therefore, as the charging / discharging cycle progresses, there are portions that are easily cracked (on the open surface side where the crystal grain size is large) and portions that are difficult to crack (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, the selective orientation plane appears on the surface of the alloy particles, so that there is a problem that the electrode catalyst ability is poor and the high rate discharge characteristics at the beginning of the charge and discharge cycle are not good. In addition, when a thin piece having a thickness of 40 μm or less is used, since the alloy particles after pulverization are fine, the contact resistance between the alloy particles is large. 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.

As described above, the metal-hydride alkaline storage battery using the hydrogen storage alloy produced by the single roll method has a drawback that the hydrogen storage alloy is easily pulverized when the charge and discharge are repeated, so that the cycle life is short. , The improvement was hoped for.

The present invention has been made in view of the above circumstances, and an object thereof is to have excellent high rate discharge characteristics, charge / discharge cycle characteristics, and overcharge resistance characteristics at the beginning of a charge / discharge cycle. (EN) Provided are a hydrogen storage alloy electrode and a method for producing the same, which makes it possible to obtain a metal-hydride alkaline storage battery.

[0014]

A hydrogen storage alloy electrode (invention electrode) for a metal-hydride alkaline storage battery according to the present invention for achieving the above object has a crystal grain defined on the roll surface side as defined below. An average thickness of 0.0 produced by a single roll method in which the minimum size is 0.2 μm or more and the maximum size of the crystal grains defined below on the open surface side is 18 μm or less.
General formula of 8 to 0.35 mm: MmR _x (Mm is Misch metal; R is Ni, Co, Al and Mn; x is 4.5 to
4.9) Mm, Ni, Co, Al
The alloy powder obtained by pulverizing the Mn alloy was used as the hydrogen storage material.

Crystal grain size: The sum of the thicknesses of these two layers in a multilayer structure in which a layer having a high concentration of rare earth elements and a layer having a low concentration of the rare earth elements appear alternately.

The ribbon-shaped Mm, Ni, Co according to the present invention
・ The thickness (average thickness) of the Al / Mn alloy ribbon is 0.08
It is regulated to ~ 0.35 mm. This is because when a ribbon having a thickness of more than 0.35 mm is used, the size of the crystal grains in the thickness direction of the ribbon is non-uniform, which leads to shortening of cycle life, while the thickness of the ribbon is reduced. If less than 0.08 mm is used, the particle surface of the alloy is oriented to the (hk0) plane and the electrode catalytic activity is reduced, leading to a reduction in high rate discharge characteristics at the beginning of the charge and discharge cycle and a short cycle life. This is because it causes The cycle life is shortened because the particle size of the alloy particles forming the electrode is small, so the contact resistance between the alloy particles in the electrode increases, and as a result, the utilization efficiency of the hydrogen storage alloy powder decreases. Is.

Further, in the present invention, Mm, Ni, Co,
The minimum crystal grain size on the roll surface side of the Al / Mn alloy is 0.2 μm or more, and the maximum crystal grain size on the open surface side is 1.
It is regulated to 8 μm or less. This is because if the minimum crystal grain size on the roll surface side is less than 0.2 μm, the hydrogen storage alloy becomes less prone to cracking, leading to a decline in high-rate discharge characteristics at the beginning of the charge / discharge cycle, and crystal formation on the open surface side. This is because if the maximum grain size exceeds 18 μm, the overcharge resistance is deteriorated. If the maximum size of the crystal grains on the open surface side exceeds 20 μm, the hydrogen storage alloy is pulverized and is prone to oxidative deterioration, which not only reduces the overcharge resistance but also reduces the cycle life. Will also be short-lived.

Mm, Ni, Co, Al, in the present invention
The Mn alloy has a general formula: MmR _x (Mm is Misch metal; R is Ni, Co, Al and Mn; x is 4.5 to 4.
It is an alloy represented by 9). When x [molar ratio of R to Mm (stoichiometric ratio)] in the general formula is out of the above range,
Overcharge resistance is reduced.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Mm / Ni / Co / Al / M
A preferable Co content of the n alloy is C based on 1 mol part of Mm.
o 0.5 to 0.9 parts by mole. If the Co content is out of this range, the overcharge resistance is deteriorated.

The electrode of the present invention has a general formula: Mm obtained by pouring the molten alloy onto the peripheral surface of a single roll that rotates at a peripheral speed of 50 to 1000 cm / sec in an inert gas or vacuum.
A ribbon-shaped Mm represented by R _x (Mm is misch metal; R is Ni, Co, Al and Mn; x is 4.5 to 4.9)
・ Ni ・ Co ・ Al ・ Mn alloy is produced, and the thin strip M
The m.Ni.Co.Al.Mn alloy is heated and held at a temperature of 750 to 950.degree. C. for a predetermined time in an inert gas or vacuum, annealed, and pulverized to prepare an alloy powder. It is prepared by coating or filling a base material (core body) with a slurry obtained by mixing the binder solution with the binder solution. Specific examples of the core include a foamed metal porous body, metal fiber, carbon fiber, metal mesh, and punching metal. 50-1000 cm / of molten alloy by single roll method
By quenching and solidifying at a roll peripheral speed of 2 seconds, the average thickness of the thin ribbon can be made 0.08 to 0.35 mm, and after quenching and solidifying, annealing is performed at a temperature of 750 to 950 ° C. The minimum grain size is 0.2 μm
As described above, the maximum can be set to 18 μm or less.

The thickness of the ribbon of the ribbon-shaped Mm, Ni, Co, Al, Mn alloy depends on the peripheral speed of the roll. When the roll peripheral speed is increased and the solidification speed is increased, the thickness of the ribbon becomes smaller. On the other hand, the size of the crystal grain depends on the temperature (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, when the annealing temperature is increased, the variation in crystal grain size is reduced. Note that when the annealing temperature exceeds 1000 ° C, the melting point of the alloy (1200
When approaching (° C.), The hydrogen storage alloy partially re-dissolves 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]

[Function] Mm / Ni / Co / Al / Mn in the present invention
Since the alloy has a thin ribbon thickness of 0.08 to 0.35 mm, the 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 thickness of the ribbon is regulated to 0.08 mm or more, the selective orientation of the grain surface of the alloy to the (hk0) plane is not so large, and the electrocatalytic activity is high.

Further, Mm, Ni, Co in the present invention
-Al-Mn alloy does not have excessively small crystal grains on the roll surface side and does not have excessive crystal grains on the open surface side.
At the beginning of the charge / discharge cycle, the alloy is appropriately cracked, and even if the charge / discharge is repeated, it does not become finely pulverized.

Furthermore, Mm.Ni.
Co / Al / Mn alloy is Ni for 1 mol part of Mm,
Since the total amount of Co, Al and Mn is regulated to 4.5 to 4.9 parts by mol, the corrosion resistance is reduced due to the pulverization of the alloy, and the utilization efficiency of the alloy is due to the fact that the alloy becomes extremely difficult to crack. Is less likely to decrease.

Therefore, the metal-hydride alkaline storage battery using the electrode of the present invention as the negative electrode is excellent in all of the high rate discharge characteristics, the charge / discharge cycle characteristics and the overcharge resistance characteristics in the initial charge / discharge cycle.

[0026]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples, and the present invention may be practiced by appropriately changing the gist of the invention. Is possible.

Reference Examples 1 to 13 [Preparation of hydrogen storage alloy] Alloy component metal (purity 9
(9.9% or more) are weighed and mixed, and after melting in a high frequency melting furnace under vacuum, single roll method (roll diameter: 350 m
m) various cooling rates shown in Table 1 (roll peripheral speed:
50, 100, 300, 500 or 1000 cm / sec)
Cooled with, composition formula: MmNi _3.1 Co _0.8 Al _0.3 M
A ribbon-shaped rare earth / nickel-based hydrogen storage alloy represented by n _0.5 (band length: about 30 to 100 mm; band width: about 20 to 50)
mm). 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.

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. 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.). The maximum and minimum crystal grain sizes are average values for 10 samples of each rare earth / nickel-based hydrogen storage alloy.

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 shown). 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 and sieved to give a maximum particle size of 100 mesh under. (In each of the following reference examples or comparative reference examples, the maximum particle size was adjusted to 100 mesh under), and a powder having an average particle size (volume-weighted average size) of 70 μm was obtained. The average particle size was determined by the 2-point method [i = 2 in the above formula (1)]. Then this powder 90
By weight, 10 parts by weight of a 2.5% by weight aqueous solution of polyethylene oxide were mixed to prepare a slurry. The average particle size was obtained by measuring the particle size distribution using a laser as a light source and a laser diffraction method utilizing the Fraunhofer diffraction phenomenon. Microtrac particle size analyzer (Leeds & Northrup, 799
Type 1) was used.

Next, this slurry was applied to a punching metal obtained by plating iron with nickel and dried to prepare 13 kinds of hydrogen storage alloy electrodes.

[Preparation of Nickel / Hydride Alkaline Storage Battery] AA was sequentially prepared by using each of the above hydrogen storage alloy electrodes as a negative electrode.
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.

Table 1 collectively shows the alloy production conditions (roll peripheral speed and annealing temperature), the thickness of the ribbon, and the maximum and minimum of the crystal grain size in Reference Examples 1 to 13.

[0035]

[Table 1]

(Comparative Reference Example 1) A massive rare earth / nickel-based hydrogen storage alloy having the same composition was produced in the same manner as in Reference Examples 1 to 13 except that a normal solidification method was used instead of the single roll method.

Then, this alloy was annealed at 900 ° C. for 6 hours (the annealing time was unified to 6 hours in the following reference examples or comparative reference examples), mechanically crushed and sieved. A powder having an average particle size of 70 μm, a maximum crystal grain size of 25 μm and a minimum crystal grain size of 7 μm was produced.

A battery B1 was produced in the same manner as in Reference Examples 1 to 13 except that this powder was used as the hydrogen storage material.

(Comparative Reference Example 2) Roll peripheral speed of 10 cm
/ Sec and the annealing temperature was 900 ° C., except that the average grain size was 70 μm, the average thickness was 0.57 μm, and the maximum crystal grain size on the open surface side was the same as in Reference Examples 1 to 13. A powder having a size of 40 μm and a minimum crystal grain size on the roll surface side of 0.2 μm was prepared.

A battery B2 was produced in the same manner as in Reference Examples 1 to 13 except that this powder was used as the hydrogen storage material.

(Comparative Reference Example 3) Roll peripheral speed of 300c
m / sec and the annealing temperature was 500 ° C., except that the average particle size was 70 μm in the same manner as in Reference Examples 1 to 13.
A powder having an average thickness of 0.27 μm, a maximum crystal grain size on the open side of 15 μm, and a minimum crystal grain size on the roll side of 0.01 μm or less was prepared.

A battery B3 was produced in the same manner as in Reference Examples 1 to 13 except that this powder was used as the hydrogen storage material.

(Comparative Reference Example 4) Roll peripheral speed of 300c
The average particle size was 70 μm in the same manner as in Reference Examples 1 to 13 except that the annealing temperature was 1200 ° C.
m, the average thickness was 0.27 μm, 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 0.4 μm.

A battery B4 was produced in the same manner as in Reference Examples 1 to 13 except that this powder was used as the hydrogen storage material.

(Comparative Reference Example 5) In the same manner as in Reference Examples 1 to 13 except that a normal solidification method (water cooling solidification method) was used in place of the single roll method, and no annealing treatment was performed.
Average grain size is 70μm, maximum grain size is 35μ
m, and the minimum powder was 10 μm.

A battery B5 was produced in the same manner as in Reference Examples 1 to 13 except that this powder was used as the hydrogen storage material.

(Comparative Reference Example 6) Roll peripheral speed of 300c
The average grain size was 70 μm, the average thickness was 0.27 μm, and the maximum crystal grain size on the open surface side was 1 in the same manner as in Reference Examples 1 to 13 except that the annealing treatment was performed at m / sec.
0 μm, the minimum crystal grain size on the roll side is 0.01
A powder having a size of μm or less was produced.

A battery B6 was produced in the same manner as in Reference Examples 1 to 13 except that this powder was used as the hydrogen storage material.

Comparative Reference Example 7 A molten alloy having the same composition as in Reference Examples 1 to 13 (MmNi _3.1 Co _0.8 Al _0.3 M)
After coagulation by n _{0. 5)} the atomization method, 900 °
Annealing was performed for 6 hours at C to prepare a hydrogen storage alloy powder. The maximum and minimum of the average grain size and the crystal grain size were 70 μm, 8 μm, and 0.1 μm, respectively.

A battery B7 was produced in the same manner as in Reference Examples 1 to 13 except that this powder was used as the hydrogen storage material.

(Comparative Reference Example 8) Roll peripheral speed is 1500
cm / sec and the annealing temperature was 900 ° C., and the average particle size was 70 μm in the same manner as in Reference Examples 1 to 13.
m, the average thickness was 0.06 μm, the maximum crystal grain size on the open surface side was 5 μm, and the minimum crystal grain size on the roll surface side was 0.2 μm.

A battery B8 was produced in the same manner as in Reference Examples 1 to 13 except that this powder was used as the hydrogen storage material.

(Comparative Reference Example 9) Roll peripheral speed was 3000
cm / sec (roll diameter: 150 mm) and the annealing temperature was 900 ° C., in the same manner as in Reference Examples 1 to 13 having an average particle diameter of 55 μm and an average thickness of 0.04 μm.
A powder having a maximum crystal grain size of 2 μm on the open surface side and a minimum crystal grain size of 0.2 μm on the roll surface side was produced. Since the peripheral speed of the roll was set to a high speed of 3000 cm / sec, a roll having an average particle diameter of 70 μm could not be obtained.

A battery B9 was prepared in the same manner as in Reference Examples 1 to 13 except that this powder was used as the hydrogen storage material.

(Comparative Reference Example 10) Roll peripheral speed is 500
The average particle size was 48 μm and the average thickness was 0.03 μm in the same manner as in Reference Examples 1 to 13 except that 0 cm / sec (roll diameter: 150 mm) and the annealing temperature was 900 ° C.
m, the maximum crystal grain size on the open surface side was 2 μm, and the minimum crystal grain size on the roll surface side was 0.15 μm. Since the roll peripheral speed was set to a high speed of 5000 cm / sec, a roll having an average particle diameter of 70 μm could not be obtained.

A battery B10 was produced in the same manner as in Reference Examples 1 to 13 except that this powder was used as the hydrogen storage material.

Table 2 shows the alloy preparation conditions (roll peripheral speed and annealing temperature), the thickness of the ribbon, and the maximum and minimum of the grain size in Comparative Reference Examples 1 to 10.

[0058]

[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. From this result, in order to obtain a hydrogen storage alloy electrode that makes it possible to provide a metal-hydride alkaline storage battery that is excellent in both high rate discharge characteristics and charge / discharge cycle characteristics in the initial charge / discharge cycle, in order to obtain a hydrogen storage alloy electrode, Minimum grain size is 0.2μ
m or more, the maximum crystal grain size on the open surface side is 20 μm or less, and the average thickness is 0.08 to 0.35 μm. It turns out that you need to use.

The batteries A1 to A13 are excellent in high rate discharge characteristics in the early stage of charge / discharge cycle and have a long service life because the hydrogen storage alloy used for the negative electrode has little segregation of Mn or 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 broken 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 broken 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 increased to 0.02 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 ribbon thinner than that 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 smaller. It has a short life.

<MmR_xChemistry of R in the x (Mm
Relationship between stoichiometric ratio) and overcharge resistance> Alloy component metal (either
(Purity 99.9% or more) is weighed and mixed,
After melting in a frequency melting furnace, single roll method (roll diameter: 3
50 mm) to cool the roll at a peripheral speed of 300 cm / sec.
And composition formula: MmNi_3.6Co_0.8Al_0.3Mn
_0.5(MmR_xX = 5.2), MmNi_3.4Co
_0.8Al_0.3Mn_0.5(MmR_xX = 5.0), M
mNi_3.3Co_0.8Al_0.3Mn_0.5(MmR_xInside x
= 4.9), MmNi_3.2Co_0.8Al_0.3Mn
_0.5(MmR_xX = 4.8), MmNi_3.1Co
_0.8Al_0.3Mn_0.5(MmR_xX = 4.7), M
mNi_3.0Co_0.8Al_0.3Mn_0.5(MmR_xInside x
= 4.6), MmNi_2.9Co_0.8Al_0.3Mn
_0.5(MmR_xX = 4.5), MmNi_2.8Co
_0.8Al_0.3Mn_0.5(MmR_xX = 4.4) or
MmNi_2.6Co_0.8Al_0.3Mn_0.5(MmR_xIn
x = 4.2) 9 kinds of ribbon-shaped Mm, Ni, C
An o.Al.Mn alloy was prepared.

Next, these strip-shaped Mm, Ni, C
o ・ Al ・ Mn alloy at 900 ° C in Ar gas 6
After annealing for a time, mechanically crushed in an inert gas (Ar gas) atmosphere to give an average particle size of 70 μm.
An alloy powder was prepared in which the maximum crystal grain size on the open surface side was 18 μm, the minimum crystal grain size on the roll surface side was 0.2 μm, and the average ribbon thickness was 0.25 mm. Table 3 collectively shows the stoichiometric ratio x ( _x in MmR _x ) of the produced alloy, the molar ratio of Ni to Mm, the thickness of the ribbon, and the maximum and minimum of the grain size.

[0075]

[Table 3]

In the same manner as in Reference Examples 1 to 13 except that these hydrogen storage alloy powders were used as the hydrogen storage material,
AA size positive electrode dominant nickel-hydride alkaline storage battery (battery capacity: 1200 mAh ± 10 mAh) A1
4 to A17 and B11 to B14 were produced.

[Overcharge Resistance Characteristics] Batteries A14 to A17 and B11 to B14 were 120 mA at room temperature (about 25 ° C.).
After charging for 16 hours at 60 ° C, 120 mA at 60 ° C.
It was discharged to 95 V and activated.

Next, each battery was 240 mA at 40 ° C.
The battery is charged at (0.2C) for 10 days, rested for 1 hour to return the ambient temperature to room temperature, and then discharged at 1.0 mA to 1.0 V. One cycle is a charge-discharge cycle test, and the discharge of each battery is performed. The capacity is 80 of the discharge capacity of the first cycle
The number of charging / discharging cycles until it decreased to below 10% was examined. The number of charge / discharge cycles was calculated for each of 10 batteries, and the overcharge resistance of each battery was evaluated by the average of 8 charge / discharge cycles excluding the smallest number of charge / discharge cycles and the largest number of charge / discharge cycles. . The results are shown in Table 3 above.
Shown in

As shown in Table 3, the stoichiometric ratio x is 4.5.
To batteries A14 to A17 using the alloy Nos. To 4.9 are batteries B1 using the alloy whose stoichiometric ratio x is outside this range.
Compared to 1 to B14, it is much superior in overcharge resistance.
It is considered that the batteries B11 and B12 did not have good overcharge resistance because the alloy did not crack easily, so the oxygen gas consumption characteristics were poor, and the electrolyte leaked out. Also,
The batteries B13 and B14 have poor overcharge resistance because the second phase (Mm ₂ R ₇ phase), which is different from the mother phase and does not cause a favorable oxygen gas consumption reaction during overcharge, causes oxidation of the alloy. Probably because it advanced. Combining the results shown in Table 3 and the above results, the minimum crystal grain size on the roll surface side is 0.2 μm or more, and the maximum crystal grain size on the open surface side is 18 μm or less. A general formula having an average thickness of 0.08 to 0.35 mm produced by the roll method: MmR _x (M
m is misch metal; R is Ni, Co, Al and Mn;
x is 4.5 to 4.9), and is a strip-shaped Mm / Ni /
By using an alloy powder obtained by pulverizing a Co / Al / Mn alloy as a hydrogen storage material, not only high rate discharge characteristics and charge / discharge cycle characteristics at the beginning of the charge / discharge cycle but also excellent overcharge resistance characteristics are obtained. It can be seen that a hydrogen storage alloy electrode is obtained which gives a metal-hydride alkaline storage battery.

<Relationship between the molar ratio of Co to Mm and the high rate discharge characteristics at the beginning of the charge / discharge cycle and the overcharge resistance characteristics> Alloy component metals (all having a purity of 99.9% or more) are weighed and mixed, and the mixture is vacuumed. After melting in a high-frequency melting furnace below, roll peripheral speed 300 by single roll method (roll diameter: 350 mm)
Cooled at cm / sec, composition formula: MmNi _2.8 Co _1.1 A
l _0.3 Mn _0.5 (molar ratio of Co to Mm 1.1),
MmNi _2.95 Co _0.95 Al _0.3 Mn _0.5 (Co molar ratio to Mm 0.95), MmNi _3.0 Co _0.9 Al
_0.3 Mn _0.5 (molar ratio of Co to Mm 0.9), M
mNi _3.2 Co _0.7 Al _0.3 Mn _0.5 (C for Mm
o molar ratio 0.7), MmNi _3.3 Co _0.6 Al _0.3 M
n _0.5 (molar ratio of Co to Mm of 0.6), MmNi
_3.4 Co _0.5 Al _0.3 Mn _0.5 (Co molar ratio to Mm 0.5), MmNi _3.5 Co _0.4 Al _0.3 Mn _0.5
(Co molar ratio to Mm 0.4) or MmNi _3.55
Eight types of ribbon-shaped MmNi · Co · represented by Co _0.35 Al _0.3 Mn _0.5 (Co molar ratio of Mm to 0.35)
An Al / Mn alloy was prepared.

Then, these ribbon-shaped MmNi.Co
The Al / Mn alloy was annealed at 900 ° C. in Ar gas for 6 hours, and then mechanically pulverized in an inert gas (Ar gas) atmosphere to prepare an alloy powder having an average particle size of 70 μm. . The molar ratio of Co to Mm of the produced alloy, the thickness of the ribbon, the maximum and minimum of the grain size are
It is summarized in Table 4.

[0082]

[Table 4]

Then, in the same manner as in Reference Examples 1 to 13 except that these alloy powders were used as the hydrogen storage material,
AA size positive electrode dominant nickel-hydride alkaline storage batteries A18 to A21 and B15 to B18 (battery capacity:
1200 mAh ± 10 mAh) was prepared.

Each nickel-hydride alkaline storage battery produced was subjected to a high rate discharge test and an overcharge resistance characteristic test under the same conditions as above, and the high rate discharge characteristic and the overcharge resistance characteristic of each battery at the beginning of the charge / discharge cycle were evaluated. Examined. The results are shown in Table 4 above. In addition, in Table 4, the results of Battery A8 (molar ratio of Co to Mm of 0.8) are transcribed from Table 3.

From Table 4, Mm / Ni / Co / Al / Mn
In the case of an alloy, in order to obtain a hydrogen storage alloy electrode that provides a nickel-hydride alkaline storage battery excellent in both high rate discharge characteristics and overcharge resistance at the beginning of a charge / discharge cycle, the molar ratio of Co to Mm is 0. 5-0.9 Mm ・ Ni ・ C
It can be seen that it is preferable to use o.Al.Mn alloy. Batteries B15 and B16 using alloys in which the molar ratio of Co to Mm is larger than 0.9 have small high-rate discharge capacity because the alloy powder has a small specific surface area. Also, Mm
B17 in which the molar ratio of Co to B is less than 0.5,
B18 has a large specific surface area and thus a large high-rate discharge capacity, but is inferior in overcharge resistance because the alloy is easily cracked and pulverized.

<Relationship between Annealing Temperature and Overcharge Resistance> Alloy component metals (purity: 99.9% or more) are weighed and mixed, and melted in a high frequency melting furnace under vacuum, followed by a single roll method. (Roll diameter: 350mm) Roll peripheral speed 30
Cooled at 0 cm / sec, compositional formula: MmNi _3.1 Co _0.8
Al _0.3 Mn _0.5 (Co molar ratio to Mm 0.8)
A ribbon-shaped Mm / Ni / Co / Al / Mn alloy represented by

Next, these ribbon-shaped Mm.Ni.C
o ・ Al ・ Mn alloys at various temperatures (700, 750, 8
00, 900, 950 or 1000 ° C.), and then annealed in Ar gas for 6 hours, and then mechanically crushed in an inert gas (Ar gas) atmosphere to obtain an average particle size of 70.
A μm alloy powder was prepared. Table 5 shows the annealing temperature, the thickness of the ribbon, and the maximum and minimum of the grain size.

[0088]

[Table 5]

Then, in the same manner as in Reference Examples 1 to 13 except that these hydrogen storage alloy powders were used as the hydrogen storage material, the AA size positive electrode dominant nickel-hydride alkaline storage batteries A22 to A24 and B19, B20 (battery capacity: 1200 mAh ± 10 mAh) was produced.

Each nickel-hydride alkaline storage battery produced was subjected to an overcharge resistance test under the same conditions as above, and the overcharge resistance of each battery was examined. The results are shown in Table 5 above. In Table 5, battery A8 (annealing temperature 900
The results of (° C) are shown by transcription from Table 3.

From Table 5, in order to obtain a hydrogen storage alloy electrode which provides a nickel-hydride alkaline storage battery excellent not only in high rate discharge characteristics and charge / discharge cycle characteristics in the early stage of charge / discharge cycle but also in overcharge resistance, , 750-950 ° C
・ Ni ・ Co ・ Al ・ M annealed at different temperatures
It can be seen that it is necessary to use n alloys.

[0092]

By using the electrode of the present invention as a negative electrode, it is possible to obtain a metal-hydride alkaline storage battery which is excellent in high rate discharge characteristics at the beginning of charge / discharge cycle, charge / discharge cycle characteristics and overcharge resistance. It will be possible. Also,
The method of the present invention makes it possible to obtain the electrode of the present invention having such excellent electrode 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 strip-shaped hydrogen storage alloy 1 White part (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 open side O crystal grain 4 Roll surface Size of crystal grain on side R 5 Thickness of ribbon

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Nobuyuki Higashiyama 2-5-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (72) Inventor Yasushi Kuroda 2-5, Keihanhondori, Moriguchi-shi, Osaka No. 5 in Sanyo Electric Co., Ltd. (72) Inventor Ikuro Yonezu 2-5-5 Keihan Hondori, Moriguchi City, Osaka Prefecture Sanyo Electric Co., Ltd. (72) Inventor Koji Nishio 2 Keihanhondori, Moriguchi City, Osaka Prefecture 5-5, Sanyo Electric Co., Ltd.

Claims (5)

[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 18 μm or less. A general formula with an average thickness of 0.08 to 0.35 mm: MmR _x (Mm is misch metal; R is Ni,
Co, Al and Mn; x is 4.5 to 4.9), and an alloy powder obtained by pulverizing a ribbon-shaped Mm / Ni / Co / Al / Mn alloy is used as a hydrogen storage material. A hydrogen-storing alloy electrode for a metal-hydride alkaline storage battery. Crystal grain size: The sum of the thicknesses of these two layers in a multilayer structure in which a layer having a high concentration of rare earth elements and a layer having a low concentration of the rare earth elements appear alternately. 2. The metal-hydride alkaline storage battery according to claim 1, wherein the Mm.Ni.Co.Al.Mn alloy contains 0.5 to 0.9 mol part of Co per 1 mol part of Mm. Hydrogen storage alloy electrode. 3. The metal-hydride alkaline storage battery according to claim 1, wherein the Mm.Ni.Co.Al.Mn alloy contains 2.9 to 3.3 parts by mole of Ni per 1 part by mole of Mm. Hydrogen storage alloy electrode. 4. The Mm.Ni.Co.Al.Mn alloy contains 0.5 to 0.9 mol part of Co and 2.9 to 3.3 mol part of Ni per 1 mol part of Mm. A hydrogen storage alloy electrode for a metal-hydride alkaline storage battery according to claim 1, which contains. 5. A roll peripheral speed of 5 in an inert gas or vacuum.
General formula: MmR _x (Mm is misch metal; R is Ni, Co, Al and Mn; x is 4.5 to 4.5) by pouring molten alloy on the peripheral surface of a single roll rotating at 0 to 1000 cm / sec
4.9) Mm, Ni, Co, Al
A Mn alloy is produced and the thin strips of Mm, Ni, Co, and Al are formed.
・ Mn alloy in an inert gas or vacuum at 750 to 950
A metal-hydride alkali, characterized in that it is annealed by heating at a temperature of ° C for a predetermined time, pulverized to produce an alloy powder, and the alloy powder is used as a hydrogen storage material to produce an electrode. A method of manufacturing a hydrogen storage alloy electrode for a storage battery.