JP2000277106A - Hydrogen storage alloy electrode for alkaline storage battery and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an alloy electrode allowing an alkaline storage battery having a good storage characteristic to be manufactured by using alloy powder provided by crushing a band-like rare earth-nickel based hydrogen storage alloy which is made by a double roll method and for which the size of its each crystalline particle is in a specific range as a hydrogen storage material. SOLUTION: A rare earth-nickel based hydrogen storage alloy for which the size of its each crystalline particle is 0.01-0.19 μm is used. An Mm.Ni.Co.Al.Mn alloy expressed by the formula MmRx (where, Mm is a misch metal; R is Ni, Co, Al and Mn; x is 4.6-5.2) is suitable. The contents of Co and Ni are preferably 0.3-0.9 pts. mol and 3.0-3.6 pts. mol with respect to one pt. mol of Mm, respectively. For instance, a band-like rare earth-nickel based hydrogen storage alloy is made by rapidly cooling and solidifying an alloy molten metal at a roll circumferential speed of 50-100 cm/sec by a double roll method in an inert gas, alloy powder is provided by performing an annealing process to it and by crushing it, and the electrode is made by mixing it with a binder solution and by applying it to an electrode base material.

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 an alkaline storage battery and a method for producing the same, and more particularly, to provide a hydrogen storage alloy electrode for providing an alkaline storage battery having good storage characteristics. The present invention relates to improvement of a hydrogen storage alloy as a hydrogen storage material.

[0002]

2. Description of the Related Art In recent years,
Alkaline storage batteries using a metal compound such as nickel hydroxide for the positive electrode and a new material hydrogen storage alloy for the negative electrode
High energy density per unit weight and unit volume,
Because of the ability to increase the capacity, it is attracting attention as a next-generation alkaline storage battery that replaces nickel-cadmium storage batteries.

As a hydrogen storage alloy for an alkaline storage battery, an alloy obtained by solidifying a molten alloy in a mold with water cooling and then pulverizing the same is used (hereinafter, this hydrogen storage alloy is referred to as a “normally solidified product”). ").

However, since usually segregation (concentration of component element concentration) is large in a solidified product, alloy particles crack when absorbing or releasing hydrogen during charge and discharge, and the specific surface area tends to increase. . For this reason, an alkaline storage battery using a normally coagulated product as a negative electrode material has good high-rate discharge characteristics at the beginning of a charge / discharge cycle, but generally has a short cycle life because a segregated portion tends to be a starting point of oxidation deterioration (corrosion). Had a problem.

As a method of improving the cycle life, it has been previously proposed to use a product obtained by subjecting a solidified product to an annealing treatment (a treatment of heating and holding at a predetermined temperature for a predetermined time) (Japanese Patent Application Laid-Open No. Sho 60/1985). -89066).

However, when an annealing treatment is usually applied to a solidified product, segregation is reduced, so that the cycle life is longer than that of an untreated product, but the segregation is reduced and the size of crystal grains is reduced. (The sum of the thicknesses of two adjacent layers in a layered structure in which a layer with a high concentration of the rare earth element and a layer with a low concentration of the rare earth appear alternately) becomes too large, so that the particles are less likely to crack, and The high-rate discharge characteristics at the beginning of the discharge cycle are significantly reduced as compared with the untreated one.

[0007] In view of the above-mentioned difficult problems to be solved in a solidified product, a hydrogen storage alloy manufactured by a roll method in which a molten alloy is ejected onto the peripheral surface of a roll rotating at a high speed and rapidly solidified has recently been used for an alkaline storage battery. (See Japanese Patent Application Laid-Open No. 6-187979).

[0008] Since the hydrogen storage alloy produced by the roll method is obtained by rapidly solidifying a molten alloy, it is hardly affected by a gravitational field when the molten alloy is solidified. Less segregation.

The roll method includes a single roll method and a twin roll method. Since the hydrogen storage alloy produced by the single roll method has a large variation in crystal grain size (difference between the maximum and minimum crystal grain sizes), it is easily broken (open side where the crystal grains are large). And a portion that is difficult to crack (the roll surface side where the crystal grain size is small).

FIG. 4 is a cross-sectional view schematically showing a state of crystal grains appearing in a cross section when the hydrogen storage alloy S1 produced by the single roll method is cut along a plane perpendicular to the band surface along the band length direction. (Only a part is described). In the figure, a white portion 41 is a layer having a high concentration of a rare earth element, a black portion 42 is a layer having a low concentration, and the sum of the thicknesses of these two adjacent layers indicates the size of a crystal grain. 45 is the thickness of the strip. As shown in FIG. 4, the size 43 of the crystal grains on the open surface side O is large, and the size 44 of the crystal grains on the roll surface side R is small. The open surface side O where the crystal grain size 43 is large is easily broken, and the roll surface side R where the crystal grain size 44 is small is hard to crack. When charge and discharge are repeated, cracks are intensively generated on the open surface O which is easily broken, and pulverization starts from the generated cracks. The new surface generated by the pulverization is easily oxidized and self-discharged during storage, which causes a deterioration in storage characteristics.

Hydrogen storage alloy S prepared by single roll method
Annealing of No. 1 increases the size of the crystal grains on the roll surface side R, thereby reducing the variation in the size of the crystal grains (see JP-A-8-213004).

FIG. 3 shows a hydrogen storage alloy S2 obtained by annealing a hydrogen storage alloy S1 obtained by rapid solidification by a single roll method and cut along a direction perpendicular to the band surface along the band length direction. FIG. 4 is a cross-sectional view schematically showing a state of crystal grains appearing in a cross section at this time (only a part is drawn). In the figure, white part 3
Reference numeral 1 denotes a layer having a high concentration of a rare earth element, black portions 32 have a low concentration, and the sum of the thicknesses of these two adjacent layers indicates the size of the crystal grains. 35 is the thickness of the strip.

However, although the variation in the crystal grain size of the hydrogen storage alloy S2 is smaller than that of the hydrogen storage alloy S1, it is still considerably large, so that it is difficult to greatly improve the storage characteristics of the hydrogen storage alloy S2. It is.

On the other hand, in the hydrogen storage alloy produced by the twin roll method, both sides of the strip (both roll sides) are rapidly solidified by rolls, so that both surface portions are compared with the central portion. The size of crystal grains is small.

FIG. 2 is a cross-sectional view schematically showing a state of crystal grains appearing in a cross section when the hydrogen storage alloy T1 produced by the twin roll method is cut along a band length direction and a plane perpendicular to the band surface. (Only a part is described). In the figure, a white portion 21 is a layer having a high concentration of a rare earth element, a black portion 22 is a layer having a low concentration, and the sum of the thicknesses of these two adjacent layers indicates the size of a crystal grain. 25 is the thickness of the strip. As shown in FIG. 2, the size of the crystal grains is smaller in both the rapidly solidified surfaces than in the central portion that is relatively slowly solidified. The central part where the crystal grain size is large is easily broken, and the surface part where the crystal grain size is small is hard to crack. For this reason, pulverization is likely to occur starting from a crack generated in the center.

As described above, all of the hydrogen storage alloys manufactured by the conventional roll method are apt to cause self-discharge because cracks are intensively generated and easily pulverized, which causes a deterioration in storage characteristics. Was.

Therefore, an object of the present invention is to provide a hydrogen storage alloy electrode which provides an alkaline storage battery having good storage characteristics, and a method for producing the same.

[0018]

In order to achieve the above object, a hydrogen storage alloy electrode for an alkaline storage battery according to the present invention (hereinafter referred to as the "electrode of the present invention") has a crystal grain size defined below. The alloy powder obtained by pulverizing a strip-shaped rare-earth / nickel-based hydrogen storage alloy produced by the twin-roll method with a minimum of 0.01 μm or more and a maximum of 0.19 μm or less is used as a hydrogen storage material. It was done.

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

The rare earth / nickel based hydrogen storage alloy according to the present invention has a minimum crystal grain size of 0.01 μm or more,
The maximum is 0.19 μm or less. The reason why the minimum and maximum are limited to the above range is as follows.

The strain caused by the expansion and contraction of the crystal lattice accompanying the occlusion and release of hydrogen appears as cracks. Cracks are likely to occur in portions where crystal grains are large, and pulverization is likely to occur starting from portions where cracks are concentrated. This means that when the crystal grains are relatively uniform in size and small in variation, cracks are dispersed and generated, so that pulverization hardly occurs. Therefore, in order to suppress the pulverization of the hydrogen storage alloy and improve the storage characteristics, it is necessary to use a hydrogen storage alloy having a small variation in crystal grain size.

A preferred rare earth / nickel based hydrogen storage alloy is represented by the general formula: MmR _x (Mm is a misch metal; R
Is Ni, Co, Al and Mn; x is an Mm-Ni-Co-Al-Mn alloy represented by 4.6 to 5.2).

The preferred Co content of the above-mentioned Mm-Ni-Co-Al-Mn alloy is such that Co0.3
０．９0.9 mol part. In addition, the above Mm-Ni-Co-
The preferred Ni content of the Al-Mn alloy is 3.0 to 3.6 mol parts Ni per 1 mol part of Mm.

The electrode of the present invention is prepared by, for example, rapidly solidifying a molten alloy by a twin roll method at a roll peripheral speed of 50 to 1000 cm / sec in an inert gas or vacuum to produce a strip-shaped rare earth / nickel hydrogen storage alloy. Then, the band-shaped rare-earth / nickel-based hydrogen storage alloy is placed in an inert gas or vacuum for 600 hours.
Annealed at a temperature of ~ 1000 ° C, pulverized to prepare an alloy powder, and a slurry obtained by mixing the alloy powder and a binder solution is applied or filled to an electrode substrate. . 50-1000 of molten alloy by twin roll method
Rapid solidification at a roll peripheral speed of cm / sec.
By annealing at a temperature of 000 ° C., the minimum of the crystal grain size is 0.01 μm or more and the maximum is 0.19 μm.
μm or less.

The size of the crystal grains depends on the annealing temperature during the annealing process. Normally, when the annealing temperature is increased, the minimum of the crystal grain size increases, but the maximum hardly changes. That is, the variation in crystal grain size is reduced by the annealing process. However, if the annealing temperature is 1000
When the melting point of the alloy approaches (about 1200 ° C.) exceeding the temperature of ° C., the crystal grain boundary of the hydrogen storage alloy partially re-melts, and becomes extremely hard to be cracked and inactivated. Annealing time is 1-10
About an hour. Usually, the effect of the annealing treatment is saturated in about 10 hours.

[0026]

The rare-earth / nickel-based hydrogen storage alloy according to the present invention is hardly pulverized and oxidized because the dispersion of crystal grains is small. For this reason, the battery of the present invention
It is hard to self-discharge and has good storage characteristics.

[0027]

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.

(Experiment 1) An electrode of the present invention and a comparative electrode were prepared, an alkaline storage battery was prepared using each of them, and the storage characteristics of each battery were examined.

[Preparation of Hydrogen Storage Alloy] Alloy component metals (all having a purity of 99.9% or more) were weighed and mixed, melted in a high-frequency melting furnace under vacuum, and then rolled by a twin roll method. After cooling at 300 cm / sec, the composition formula: MmNi
_3.4 Strip-shaped rare earth / nickel-based hydrogen storage alloy represented by Co _0.8 Al _0.3 Mn _0.5 (thickness of strip: about 0.1 m)
m) was prepared.

Next, the rare-earth / nickel-based hydrogen storage alloy was heated at various temperatures (500, 600, 70
0, 800, 900, 1000 and 1100 ° C.)
Annealing was performed in an Ar atmosphere for 6 hours.

Each of the annealed rare earth / nickel-based hydrogen storage alloys is cut perpendicularly to the band surface along the band length direction, and the cross section reflected electron beam image is taken by a scanning electron microscope (manufactured by JEOL Ltd. "JEOL866")
The maximum crystal grain size and the minimum crystal grain size were determined. The maximum and minimum are both average values for 10 samples of each alloy. Table 1 shows the maximum and minimum crystal grain sizes of each alloy.

FIG. 1 shows an annealed hydrogen storage alloy T
FIG. 2 is a cross-sectional view schematically showing a state of crystal grains appearing in a cross section when No. 2 is cut along a plane perpendicular to the band surface along the band length direction (only a part is drawn). In the figure, a white portion 11 is a layer having a high concentration of a rare earth element, a black portion 12 is a layer having a low concentration, and the sum of the thicknesses of these two adjacent layers indicates the size of a crystal grain. 15 is the thickness of the strip. As shown in FIG. 1, the size of the crystal grains at the surface portion is increased by the annealing process. As a result, the variation in the size of the crystal grains at the surface portion and the central portion is caused by the hydrogen storage alloy T1 ( (See FIG. 2).

[Preparation of hydrogen storage alloy electrode] Each of the above-mentioned annealed alloys is mechanically pulverized in an Ar atmosphere.
The mixture was sieved to obtain a powder having an average particle size of about 60 μm and a maximum particle size of 100 mesh or less (in the following experiments, the maximum particle size was all adjusted to 100 mesh or less). Then
10 parts by weight of this alloy powder and 5 parts of polyethylene oxide
A slurry was prepared by mixing with 1 part by weight of a 1% by weight aqueous solution, and this slurry was applied to a punching metal formed by nickel plating on iron, dried, and rolled to produce hydrogen storage alloy electrodes E1 to E7. . Hydrogen storage alloy electrodes E2 to E
Reference numeral 6 denotes an electrode of the present invention, and the hydrogen storage alloy electrodes E1 and E7
Is a reference electrode.

[Preparation of Alkaline Storage Battery] The above-mentioned hydrogen storage alloy electrodes E1 to E7 were used as negative electrodes, and AA size positive-electrode capacity regulated alkaline storage batteries (battery capacity: 1200 mA)
h) A1 to A7 were prepared. A conventionally known sintered nickel electrode was used as the positive electrode, a nonwoven fabric made of polyamide was used as the separator, and a 30% by weight aqueous solution of potassium hydroxide was used as the alkaline electrolyte.

<Storage Characteristics> The batteries A1 to A7 were stored at 25 ° C.
The battery was charged at 120 mA for 16 hours, left at 60 ° C. for 24 hours, returned to 25 ° C., discharged to 1.0 V at 120 mA, and activated.

Each battery was subjected to 120 mA at 25 ° C.
(0.1C) for 16 hours, 1200mA (1C)
And discharged to 1.0 V to determine a discharge capacity C1. Next, each battery was charged at 120 mA (0.1 C) for 16 hours, stored at 40 ° C. for 15 days, returned to 25 ° C.,
Discharging was performed at 1200 mA to 1.0 V to obtain a discharge capacity C2, and a ratio P of the discharge capacity C2 to the discharge capacity C1 was obtained.
[(C2 / C1) × 100] was calculated. The ratio P was determined for each of the five batteries, and the storage value of each battery was evaluated using the average value. Discharge capacity C2 and ratio P of each battery
Are shown in Table 1.

[0037]

[Table 1]

As shown in Table 1, the electrodes E2 to E6 of the present invention
The batteries A2 to A6 using the comparative electrode E1 have a large ratio P of 86 to 89% and have good storage characteristics, whereas the batteries A1 using the comparative electrode E1 have a small ratio P of 73% and have poor storage characteristics. . The reason that the storage characteristics of the battery A1 are not good is that the minimum size of the crystal grains is small, so that the variation in the size of the crystal grains is large, and cracks are intensively generated in a portion where the crystal grains are large. It is considered that pulverization occurred from the part as a starting point. The reason why the discharge capacity C2 after storage of the battery A1 is small is that the alloy was not sufficiently activated because the annealing temperature was too low.
Battery A7 using comparative electrode E7 has a large ratio P of 85% and good storage characteristics. This is considered to be because the alloy was hardly cracked due to partial re-melting at the crystal grain boundaries and hardly oxidized. However, the discharge capacity C2 of the battery A7 after storage is much smaller than that of the batteries A2 to A6.
This is considered to be due to the fact that the alloy was hard to be cracked and was hardly activated, so that the utilization rate of the alloy was reduced.

(Experiment 2) Mm-Ni-Co-Al-Mn
The relationship between the Co content of the alloy and the cycle life was examined.

[0040] Experiment except for variously changing the Co content of the alloy component in the metal 1 (roll peripheral speed: 300 cm / sec) and the same way the composition _{formula: MmNi 4.2-y Co y Al} 0.3 Mn 0.5
Six kinds of hydrogen storage alloy powders represented by (y = 0.2, 0.3, 0.5, 0.7, 0.9 or 1.0) were produced.

Next, hydrogen storage alloy electrodes E8 to E13 and alkaline storage batteries A8 to A13 were prepared in the same manner as in Experiment 1, except that each of these hydrogen storage alloy powders was used as a hydrogen storage material.

Each of the produced alkaline storage batteries was subjected to a charge / discharge test under the same conditions as those performed in Experiment 1, and the storage characteristics of each battery were examined. Each battery after the activation treatment under the same conditions as those performed in Experiment 1 was 1200 mA
, And the internal pressure of the battery at the time of 150% charging was examined. The battery internal pressure was measured by attaching a pressure gauge to the bottom of the battery can. Table 2 shows the results. Table 2 also shows the results for Battery A4 produced in Experiment 1.

[0043]

[Table 2]

From Table 2, it can be seen that Mm-Ni-Co-Al-Mn
In the case of an alloy, it can be seen that it is preferable to use an alloy containing 0.3 to 0.9 mol part of Co with respect to 1 mol part of Mm in order to obtain an alkaline storage battery excellent in both storage characteristics and internal pressure characteristics. . It is considered that the reason why the internal pressure of the battery after the overcharge of the battery A8 is high is that the oxygen content is reduced due to the occurrence of cracks due to the insufficient Co content and the oxidation of the alloy surface. Further, it is considered that the reason why the battery internal pressure after the overcharge of the battery A13 is high is that the alloy is difficult to be cracked due to the excessive Co content, the activity is reduced, and the oxygen gas absorbing ability is reduced.

(Experiment 3) Mm-Ni-Co-Al-Mn
The relationship between the Ni content of the alloy and the cycle life was examined.

The alloys except that the components were changed variously amount of Ni in the metal Experiment 1 (roll peripheral speed: 300 cm / sec) and the same way the composition formula: MmNi _z Co _0.8 Al _0.3 Mn
_0.5 (z = 2.8, 3.0, 3.2, 3.6 or 3.
8) Hydrogen storage alloy powders represented by 8) were produced.

Then, except that these hydrogen storage alloy powders were used as the hydrogen storage material,
Hydrogen storage alloy electrodes E14 to E18 and alkaline storage battery A
14 to A18 were produced.

For each of the manufactured alkaline storage batteries, a charge / discharge test was performed under the same conditions as those performed in Experiment 1, and the storage characteristics of each battery were examined. Table 3 shows the results. Table 3 also shows the results for battery A4.

[0049]

[Table 3]

From Table 3, it can be seen that Mm / Ni / Co / Al / Mn
In the case of an alloy, it can be seen that in order to obtain an alkaline storage battery having good storage characteristics, it is preferable to use an alloy containing 3.0 to 3.6 mol parts of Ni with respect to 1 mol part of Mm.

In the above embodiment, Mm.Ni.Co.Al
-Although the Mn alloy has been described as an example, in the case of a rare earth / nickel-based hydrogen storage alloy, since the distribution of the rare earth element at the time of solidification tends to be common even if the composition is different, the present invention
The present invention can be widely applied to a hydrogen storage alloy electrode using a rare earth / nickel-based hydrogen storage alloy as a hydrogen storage material.

[0052]

The present invention provides a hydrogen storage alloy electrode which provides an alkaline storage battery having good storage characteristics.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a state of crystal grains appearing in a cross section of a band-shaped hydrogen storage alloy T2 that has been rapidly solidified by a twin roll method and then annealed.

FIG. 2 is a schematic diagram showing crystal grains appearing in a cross section of a band-shaped hydrogen storage alloy T1 that has not been annealed after being rapidly solidified by a twin-roll method.

FIG. 3 is a schematic diagram showing crystal grains appearing in a cross section of a band-shaped hydrogen storage alloy S2 which has been rapidly solidified by a single roll method and then annealed.

FIG. 4 is a schematic diagram showing crystal grains appearing in a cross section of a band-shaped hydrogen storage alloy S1 that has not been annealed after being rapidly solidified by a single roll method.

[Explanation of symbols]

T2 Strip-shaped hydrogen storage alloy which has been rapidly solidified by the twin-roll method and then annealed. 11 White portion (layer with high concentration of rare earth element) 12 Black portion (layer with low concentration of rare earth element) 15 Thickness of strip

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Katsuhiko Niiyama 2-5-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (72) Tadayoshi Tanaka 2-chome Keihanhondori, Moriguchi-shi, Osaka No. 5-5 Sanyo Electric Co., Ltd. (72) Inventor Toshiyuki Noma 2-5-5 Sanyo Electric Co., Ltd. (72) Inventor Ikuo Yonezu Keihanmoto, Moriguchi City, Osaka 2-5-5, Sanyo Electric Co., Ltd. F-term (reference) 5H003 AA03 BA00 BA01 BA04 BB02 BC01 BD00 BD01 BD03

Claims (6)

[Claims] 1. A strip-shaped rare-earth / nickel-based hydrogen-absorbing alloy produced by a twin-roll method, having a minimum grain size of 0.01 μm or more and a maximum of 0.19 μm or less as defined below, A hydrogen storage alloy electrode for an alkaline storage battery, wherein an alloy powder obtained by pulverization is used as a hydrogen storage material. Crystal grain size: The sum of the thicknesses of two adjacent layers in a multilayer structure in which layers with a high concentration of rare earth elements and layers with a low concentration of the rare earth elements appear alternately. 2. The rare earth / nickel hydrogen storage alloy according to claim 1,
General formula: MmR _x (Mm is misch metal; R is Ni,
The hydrogen storage alloy electrode for an alkaline storage battery according to claim 1, wherein Co, Al, and Mn; x is an Mm-Ni-Co-Al-Mn alloy represented by 4.6 to 5.2). 3. The hydrogen storage alloy electrode for an alkaline storage battery according to claim 2, wherein said Mm.Ni.Co.Al.Mn alloy contains 0.3 to 0.9 mol part of Co with respect to 1 mol part of Mm. . 4. The hydrogen storage alloy electrode for an alkaline storage battery according to claim 2, wherein said Mm.Ni.Co.Al.Mn alloy contains 3.0 to 3.6 mol parts of Ni with respect to 1 mol part of Mm. . 5. An alkaline storage battery having the hydrogen storage alloy electrode according to claim 1 as a negative electrode. 6. A roll peripheral speed of 5 in an inert gas or vacuum.
A molten alloy is poured into the peripheral surface of a twin roll rotating at 0 to 1000 cm / sec to produce a strip-shaped rare earth / nickel-based hydrogen storage alloy, and the strip-shaped rare earth / nickel-based hydrogen storage alloy is placed in an inert gas or vacuum. An alkaline storage battery characterized in that it is heated and held at a temperature of 600 to 1000 ° C. for a predetermined time, annealed, pulverized to produce an alloy powder, and an electrode is produced using the alloy powder as a hydrogen storage material. Production method of hydrogen storage alloy electrode for use.