JPH08134566A - Hydrogen storage alloy and hydrogen storage alloy electrode - Google Patents

Abstract

PURPOSE: To obtain a hydrogen storage alloy giving an electrode maintaining high capacity, less liable to dissolution in an alkali electrolytic soln. and excellent in preservability at high temp. CONSTITUTION: This hydrogen storage alloy is represented by the formula ZrMna Vb Mx Coy Niz (where M is at least one kind of element selected from among Al, Cr, Fe, Cu and Zn, 0.4<=a<=0.8, 0.05<=b<=0.3, 0<=x<=0.3, 0.2<y<=0.5, 0.8<=z<=1.3 and 2.0<=a+b+x+y+z<=2.4) or the formula Zr1.2-w Tiw Mna Vb Mx Coy Niz (where M is the M in the above-mentioned formula, 0<w<=0.6, 0.4<=a<=0.8, 0.1<=b<=0.4, 0<=x<=0.3, 0.2<y<=0.5, 0.8<=z<=1.3 and 1.7<=(a+ b+x+y+z)/1.2<=2.2) and the base of the alloy phase is C15 (MgCu2 ) type Laves phase.

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 capable of reversibly electrochemically storing and releasing hydrogen, and an electrode using the alloy or a hydride thereof.

[0002]

2. Description of the Related Art A hydrogen storage alloy electrode using a hydrogen storage alloy capable of reversibly absorbing and releasing hydrogen has a theoretical capacity density higher than that of a cadmium electrode, and does not cause deformation such as a zinc electrode or formation of dendrites. Therefore, it is expected as a negative electrode that provides a long life, pollution-free, and high energy density alkaline storage battery. The alloy used for the hydrogen storage alloy electrode is usually produced by an arc melting method, a high frequency induction heating melting method, or the like, and generally, Ti-Ni-based and La (or Mm) -Ni-based multi-component alloys are well known. Has been. The Ti-Ni-based multi-component alloy is classified as an AB type (A: an element having a high affinity with hydrogen such as La, Zr, and Ti, and B: a transition element such as Ni, Mn, and Cr). The AB type alloy has a characteristic that it exhibits a relatively large discharge capacity at the beginning of the charge / discharge cycle, but there is a problem that it is difficult to maintain the capacity for a long time when the charge / discharge is repeated. Further, the AB ₅ type La (or Mm) -Ni-based multi-component alloys have been extensively developed in recent years as electrode materials, and in particular, the Mm-Ni-based multi-component alloy has already been put into practical use. This La (or Mm)
The Ni-based multi-component alloy also has problems such as relatively small discharge capacity, insufficient life performance as a battery electrode, and high material cost. Therefore, a novel hydrogen storage alloy material having a large discharge capacity and a long life is desired.

On the other hand, the AB ₂ type Laves phase alloy has a relatively high hydrogen storage capacity and is promising as an electrode material having a high capacity and a long life. Many alloys such as Zr-Mn-V-Cr-Ni alloys have already been proposed for this alloy system. However,
When an AB ₂ type Larbus phase alloy is used for the electrode, T
Although the discharge capacity is larger than that of the i-Ni-based or La (or Mm) -Ni-based multi-component alloy, there is a problem that the discharge characteristics at the beginning of the charge / discharge cycle are very poor.

Therefore, by adjusting the composition with a Zr-Mn-VM-Ni-based alloy (M is at least one element selected from Fe or Co), the initial discharge characteristics are maintained while maintaining a high capacity. Has been proposed (Japanese Patent Laid-Open No. Hei 5)
-82125). There is also a proposal that the high temperature storage characteristics are improved without impairing the initial discharge characteristics by adding a small amount of Cr (JP-A-5-347156).

[0005]

However, when a sealed battery is constructed by using the electrode made of the alloy proposed by the former, the elution of the alloy component into the alkaline electrolyte is violent, so that the eluted element is conductive. There is a problem that a short circuit occurs due to precipitation in the form of oxide or the like. Further, if the battery is left at a high temperature of about 65 ° C., there is a problem that the battery voltage immediately drops. When the latter alloy containing Cr is used, the high temperature storage characteristics are improved, but there is a disadvantage that the battery voltage decreases when the storage period at a high temperature of about 65 ° C. exceeds 30 days. Nowadays, ensuring the reliability of the battery is the most important issue, and it is required to operate normally even when the period of standing at high temperature for 60 days has passed. In view of the above, the present invention has further improved high temperature storage characteristics,
An object of the present invention is to provide a hydrogen storage alloy and an electrode that provide an alkaline storage battery having high reliability.

[0006]

Means for Solving the Problems] hydrogen storage alloy of the present invention at least has the general formula _{ZrMn a V b M x Co y} Ni z ( however, M is Al, Cr, Fe, selected from the group consisting of Cu and Zn One element, 0.4 ≦ a ≦ 0.
8, 0.05 ≦ b ≦ 0.3, 0 ≦ x ≦ 0.3, 0.2 <
y ≦ 0.5, 0.8 ≦ z ≦ 1.3, and 2.0 ≦ a + b
+ X + y + z ≦ 2.4) and the main component of the alloy phase is C
It is a 15 (MgCu ₂ ) type Larvus phase. The hydrogen storage alloy of the present invention have the general formula _{Zr 1.2-w Ti w Mn a} V b M x
Co _y Ni _z (where M is at least one element selected from the group consisting of Al, Cr, Fe, Cu and Zn, and 0 <w ≦ 0.6, 0.4 ≦ a ≦ 0.8, 0.1 ≦
b ≦ 0.4, 0 ≦ x ≦ 0.3, 0.2 <y ≦ 0.5,
0.8 ≦ z ≦ 1.3, and 1.7 ≦ (a + b + x + y +
z) /1.2≦2.2), and the main component of the alloy phase is C
It is a 15 (MgCu ₂ ) type Larvus phase.

In the above general formula, it is preferable that y + z ≦ 1.5. In addition, the alloy, after the alloy production,
1000 in vacuum or in an inert gas atmosphere
It is preferably subjected to homogenizing heat treatment at ˜1300 ° C. for at least 1 hour. Further, the hydrogen storage alloy electrode of the present invention is composed of the above hydrogen storage alloy or a hydride thereof.

[0008]

The hydrogen storage alloy of the present invention is an improvement of the conventional Zr-based Larvus phase alloy and the Zr-Ti-based Lavus phase alloy, respectively. By increasing the amount of Co in the alloy, Compared with this, pulverization of the alloy is suppressed, and elution of the alloy composition into the alkaline electrolyte is reduced. Co amount, that is, y in the above general formula
When the ratio exceeds 0.2, the effect of suppressing pulverization appears, and the alloy grain size does not fall below a certain level even if the hydrogen storage-release cycle is repeated. Therefore, the new surface that appears due to the cracking of the alloy decreases, and the elution of alloy components into the alkaline electrolyte also decreases. Therefore, an alkaline storage battery configured using the electrode of the present invention, for example, a nickel-hydrogen storage battery,
It is possible to further improve the high temperature storage characteristics as compared with the conventional battery of this type. Further, since the pulverization of the alloy is suppressed, the alloy does not deteriorate even if the charge / discharge cycle is repeated, and stable performance can be maintained for a long time. However, when the Co amount y exceeds 0.5, the plateau pressure of the PCT curve (hydrogen pressure-composition isotherm) increases and the discharge capacity decreases. Therefore, the range of the Co amount y is 0.2 <y ≦ 0.
5 is suitable. The composition range other than Co is mainly 350 mA
It is determined from the viewpoint of ensuring a discharge capacity of at least h / g.
To make a high capacity battery, the capacity of the negative electrode is 350m.
About Ah / g is necessary.

[0009] First, the general formula _{ZrMn a V b M x Co y} Ni z
The Zr-based alloy represented by will be described. V is an element having a high affinity for hydrogen and contributes to an increase in hydrogen storage-release amount. However, if the V amount b is less than 0.05, the effect of V does not appear. Further, when b exceeds 0.3, the homogeneity of the alloy is deteriorated and conversely the hydrogen storage-release amount is reduced. Therefore, the V amount b is preferably 0.05 ≦ b ≦ 0.3. N
i causes a decrease in the amount of hydrogen storage-release, but contributes to the improvement of the electrochemical activity for hydrogen storage-release.
Generally, when the Ni content z is less than 1.0, the electrochemical activity is poor and the discharge capacity is reduced, but as with Ni, Co, which contributes to the improvement of the electrochemical hydrogen storage-release activity, is 0. .2 <y ≦ 0.5, the Ni content z should be 0.8 or more. However, when z is larger than 1.3, the plateau pressure increases and the hydrogen storage-release amount decreases. Therefore, the Ni amount z is 0.8 ≦
z ≦ 1.3 is suitable. Further, Ni and Co are similar elements in that they have an activity for electrochemical hydrogen storage-release, and if the Ni + Co amount (y + z) is 1.5 or less, the hydrogen storage-release amount is particularly large. Become. Therefore, it is desirable that y + z ≦ 1.5.

Mn affects the flatness of the plateau region in the PCT curve, and when the Mn amount a is 0.4 or more, the flatness becomes very good and the discharge capacity increases. But,
When the Mn amount a exceeds 0.8, Mn is apt to be eluted into the electrolytic solution and the effect of suppressing pulverization does not appear. Therefore, Mn
The amount a is preferably 0.4 ≦ a ≦ 0.8. M (Al, C
(r, Fe, Cu, Zn) is an element that suppresses a decrease in discharge capacity due to charge / discharge cycles, and is effective when the M amount x is 0.3 or less. However, when the M content x exceeds 0.3, the homogeneity of the alloy is reduced, the plateau pressure is increased, and the discharge capacity is reduced. Therefore, 0 ≦ x ≦ 0.3 is appropriate. When the ratio of the number of B-site atoms to the number of A-site atoms (a + b + x + y + z) is 2.0 or more, the homogeneity of the alloy is greatly improved and the discharge capacity is increased. However, when it is larger than 2.4, the plateau pressure rises because the crystal lattice constant becomes very small, and the discharge capacity decreases. Therefore, it is appropriate that 2.0 ≦ a + b + x + y + z ≦ 2.4.

[0011] Then the general formula _{Zr 1.2-w Ti w Mn a} V b M x C
It explained o _y Ni _z Zr-Ti-based alloys represented by. In this alloy, Ti is an element that occupies the A site like Zr. Since the atomic radius of Ti is small, when the amount of Ti becomes larger than the amount of Zr, the crystal lattice constant of the alloy becomes extremely small, so that the amount of hydrogen absorption-desorption greatly decreases. Therefore, the Ti content needs to be smaller than the Zr content. Since the inclusion of Ti lowers the crystal lattice constant as compared with the Zr-based alloy, it is necessary to increase the upper limit and the lower limit of the amount of V having a large atomic radius. Therefore, the V amount b is appropriately 0.1 ≦ b ≦ 0.4. Mn, M, and Ni are the same as in the case of the Zr-based alloy described above. The ratio (a + b + x + y + z / 1.2) of the number of B-site atoms to the number of A-site atoms is preferably 2.2 or less because the crystal lattice constant lowers when it exceeds 2.2 because it contains Ti. Even if the lower limit is lowered to 1.7, the homogeneity of the alloy is not significantly reduced. Therefore, 1.7 ≦ (a + b + x + y + z) / 1.
2 ≦ 2.2 is suitable.

In both Zr-based alloys and Zr-Ti-based alloys, homogenization heat treatment after alloy preparation improves the homogeneity and crystallinity of the alloys, resulting in a particularly large discharge capacity. However, if the heat treatment temperature is lower than 1000 ° C., the heat treatment has no effect and
If it is higher than 0 ° C., a large amount of Mn is evaporated and the alloy composition is largely deviated, so that the discharge capacity is decreased. If the heat treatment time is shorter than 1 hour, the effect of heat treatment does not appear. Further, in order to prevent the alloy from being oxidized, the heat treatment is preferably performed in vacuum or in an inert gas atmosphere. Therefore, after alloy production,
It is preferable to perform homogenizing heat treatment for 1 hour or more in a vacuum of 1000 to 1300 ° C. or in an inert gas atmosphere.

[0013]

EXAMPLES The present invention will be described in more detail below by way of its examples. Example 1 Commercially available Zr, Mn, V, Co, Ni, A
Alloys having the compositions shown in Table 1 were prepared by heating and melting each metal of 1, 1, Fe, Cu, and Zn in an argon atmosphere in an arc melting furnace. However, if the Mn amount a is 0.8 or more, a large amount of Mn evaporates when it is produced in an arc furnace, and it is difficult to obtain the target alloy.
It was produced in an induction heating furnace. Next, heat treatment was performed in vacuum at 1100 ° C. for 12 hours to obtain an alloy sample.

[0014]

[Table 1]

Sample No. 1 to 7 are comparative examples, sample N
o. 8 to 22 are some examples of the hydrogen storage alloy of the present invention. First, the degree of progress of pulverization was examined.
In Table 1, the sample No. The alloys 1 to 22 were placed in a stainless steel measuring container, degassed with a rotary pump at 150 ° C., hydrogen was absorbed at 20 ° C., and hydrogen was released at 150 ° C. After repeating 75 cycles, the alloys were It was taken out and the average particle size was measured. As a result, the sample No. with a small amount of Co. Samples 4 and 5 were finely pulverized to about 10 microns, whereas sample N containing a large amount of Co
o. It was found that the particle sizes of 1 to 3 and 6 to 22 maintain a particle size of about 20 to 25 microns.

Next, the sample No. The alloys 1 to 22 were subjected to a single cell test in order to evaluate the electrode characteristics as a negative electrode for an alkaline storage battery by an electrochemical charge / discharge reaction. The alloy was pulverized to a particle size of 300 mesh or less, 1 g of this alloy powder, 3 g of carbonyl nickel powder as a conductive agent and 0.12 g of polyethylene fine powder as a binder were thoroughly mixed and stirred, and the diameter was obtained by pressing. It was molded into a disk shape having a thickness of 24.5 mm and a thickness of 2.5 mm.
This was heated in vacuum at 130 ° C. for 1 hour to melt the binder to obtain a hydrogen storage alloy electrode. A negative electrode having a nickel wire lead attached to the hydrogen storage alloy electrode was combined with a positive electrode made of a sintered nickel electrode having an excessive capacity and a separator made of a polyamide nonwoven fabric to have a specific gravity of 1.
Charging and discharging were repeated at a constant current at 25 ° C. in an electrolytic solution containing 30 potassium hydroxide aqueous solution, and the discharge capacity in each cycle was measured. It should be noted that charging was performed at 100 mA / g of hydrogen storage alloy for 5 hours, and discharging was similarly performed at 1 mA.
It was performed at 50 mA / g and cut at 0.8V. Sample No. 1 to 3, 6 and 7 have small discharge capacities and 250 to 3
It was 00 mAh / g. Sample No. Sample No. 1 had a large amount of Mn, so that the discharge capacity was greatly deteriorated by the cycle,
o. In Nos. 2, 3 and 6, the hydrogen storage capacity itself was small, so the discharge capacity was also small. In addition, the sample No. It is considered that since No. 7 had a small amount of Ni, its activity for electrochemical hydrogen storage-release was small, and the discharge capacity was reduced. For these, the sample No. 4, 5, 8 to 22 are all 350
It was found to exhibit a discharge capacity of ~ 380 mAh / g.

Further, using these hydrogen storage alloys,
A sealed nickel-hydrogen storage battery was produced by the method as shown below. Sample No. shown in Table 1 The alloys 1 to 22 were crushed to 300 mesh or less, and mixed and stirred with a dilute aqueous solution of carboxymethyl cellulose (CMC) to form a paste, and the electrode support had an average pore size of 150 microns, a porosity of 95%, and a thickness of 1 It was filled in a foamed nickel sheet of 0.0 mm. This was dried at 120 ° C., pressed with a roller press, and further coated on its surface with a fluororesin powder to form a hydrogen storage alloy electrode. Each of these electrodes has a width of 3.3 cm, a length of 21 cm, and a thickness of 0.40 m.
The lead plate was attached at two predetermined places. Then, it was spirally wound in combination with a positive electrode and a separator having a capacity of 3.0 Ah and housed in an SC size battery case. The positive electrode at this time was a known foaming nickel electrode, and had a width of 3.3 cm and a length of 18 cm. This positive electrode also had lead plates attached at two positions. Also,
A polypropylene non-woven fabric having hydrophilicity was used as the separator, and an electrolyte solution was prepared by dissolving 30 g / l of lithium hydroxide in an aqueous potassium hydroxide solution having a specific gravity of 1.20. The battery case containing the electrode group and the electrolytic solution as described above was sealed to form a sealed battery.

The battery thus produced was charged to 150% at 0.5 ° C. (2 hour rate) at 20 ° C.,
20 cycles of charging and discharging at 0.2 C (5 hour rate) to a final voltage of 1.0 V were repeated and then left in an atmosphere of 65 ° C. FIG. 1 shows the voltage of each battery plotted against the storage period. The numbers in the figure indicate the sample No. of Table 1. Is consistent with Sample No. Samples Nos. 1 and 4 had a storage period of 20 days and sample No. In No. 5, when the storage period passed 30 days, the battery voltage dropped sharply. Sample No. Since No. 1 has a large amount of Mn, even if the amount of Co is increased to suppress pulverization, the elution of Mn cannot be suppressed. It is considered that Nos. 4 and 5 could not suppress the elution of the alloy components because the pulverization proceeded due to the small amount of Co. On the other hand, sample N
o. It was found that Nos. 2, 3, and 6 to 22 contained Co amount y of 0.3 or more, so that pulverization was suppressed, and the decrease in battery voltage was very small even after storage for 60 days. Also, Co
Sample No. with a large amount It was found that 2, 3, 6 to 22 can maintain stable performance even after 300 cycles. As described above, when the results of the pulverization experiment, the single cell test, and the high temperature storage test are combined, the alloy No. 8-22
It has a discharge capacity of 350 mAh / g or more, and it is found that the battery voltage drop is very small even after 60 days of high temperature storage.

Example 2 Commercially available Zr, Ti, Mn,
Alloys having the compositions shown in Table 2 were prepared by heating and melting each metal of V, Co, Ni, Al, Fe, Cu, and Zn in an argon atmosphere in an arc melting furnace. However, when the Mn amount a is 0.8 or more, a large amount of Mn evaporates when it is manufactured in an arc furnace, and it is difficult to obtain the target alloy. Therefore, it was manufactured in an induction heating furnace. Next, heat treatment was performed in vacuum at 1100 ° C. for 12 hours to obtain an alloy sample.

[0020]

[Table 2]

Sample No. Sample Nos. 23 to 30 are comparative examples. 31 to 46 are some examples of the hydrogen storage alloy of the present invention. First, as in Example 1, the sample N in Table 2 was used.
o. The degree of progress of pulverization was examined for alloys 23 to 46. As a result, the sample No. with a small amount of Co. Two
Samples Nos. 6 and 27 are finely pulverized up to about 10 microns, while Sample No. 6 having a large amount of Co. 23-25, 28-46
Was found to maintain a particle size of about 20 to 25 microns.

Next, sample No. With respect to the alloys Nos. 23 to 46, a unit cell test was conducted in order to evaluate the electrode characteristics as the negative electrode for alkaline storage batteries by the electrochemical charge / discharge reaction. The test method is the same as in Example 1. Sample N
o. 23 to 25 and 28 to 30 have a small discharge capacity,
It was 0 to 300 mAh / g. Sample No. 23 is Mn
Due to the large amount, the deterioration of the discharge capacity due to the cycle is large. Since 24, 25, 28, and 30 had a small hydrogen storage amount, the discharge capacity was also small. In addition, the sample No. It is considered that since No. 29 had a small amount of Ni, its activity for electrochemical hydrogen storage-release was small, and the discharge capacity was reduced. On the other hand, the sample No. 26, 27,
It was found that all of 31 to 46 have a discharge capacity of 350 to 380 mAh / g.

Further, the sample No. shown in Table 2 was used. 23-4
Using the alloy of No. 6, a sealed nickel-hydrogen storage battery was prepared in the same manner as in Example 1, and at 20 ° C., 0.5 C
Charged 150% at (2 hour rate), 0.2C (5 hour rate)
20 cycles of charging / discharging for discharging to a final voltage of 1.0 V were repeated and then left in an atmosphere of 65 ° C. FIG. 2 shows changes in each battery voltage due to storage. The numbers in the figure are Table 2
Sample No. Is consistent with Sample No. 23 and 26 have a storage period of 20 days and sample No. In No. 27, the battery voltage dropped sharply after the storage period of 30 days. Sample No. No. 23 has a large Mn content, so even if the Co content is increased to suppress pulverization, the elution of Mn cannot be suppressed. It is considered that 26 and 27 did not suppress the elution of the alloy composition due to the progress of pulverization due to the small amount of Co. On the other hand, the sample No. 24, 25, 28-
It was found that 46 has a Co content y of 0.3 or more, so that pulverization is suppressed, and that the battery voltage drop is very small even after storage for 60 days. In addition, Sample No. with a large amount of Co.
It was found that 24, 25, 28 to 46 can maintain stable performance even after 300 cycles. As described above, when the results of the pulverization experiment, the single cell test, and the high temperature storage test are combined, the alloy No. 31-46 is 350 mA
It was found that the battery had a discharge capacity of h / g or more, and the battery voltage dropped very little even after 60 days of high temperature storage.

[0024]

EFFECTS OF THE INVENTION The hydrogen storage alloy of the present invention suppresses pulverization due to charge and discharge, and less elution of alloy components into the alkaline electrolyte. Therefore, the alkaline storage battery using this alloy as the negative electrode can have further improved high-temperature storage characteristics and excellent cycle life characteristics as compared with conventional batteries of this type.

[Brief description of drawings]

FIG. 1 is a diagram showing changes in battery voltage during storage at 65 ° C. of storage batteries using hydrogen storage alloy electrodes of Examples and Comparative Examples of the present invention.

FIG. 2 is a diagram showing changes in battery voltage during storage at 65 ° C. of a storage battery using hydrogen storage alloy electrodes of other examples and comparative examples of the present invention.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoichiro Tsuji 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (5)

[Claims] 1. A general formula _{ZrMn a V b M x Co y} Ni z ( however, M is at least one element selected Al, Cr, Fe, from the group consisting of Cu and Zn, 0.4 ≦
a ≦ 0.8, 0.05 ≦ b ≦ 0.3, 0 ≦ x ≦ 0.3,
0.2 <y ≦ 0.5, 0.8 ≦ z ≦ 1.3, and 2.0
≦ a + b + x + y + z ≦ 2.4), and the main component of the alloy phase is a C15 (MgCu ₂ ) type Larvus phase, a hydrogen storage alloy. 2. The general formula Zr _1.2-w Ti _w Mn _a V _b M _x Co _y.
Ni _z (where M is Al, Cr, Fe, Cu and Z
at least one element selected from the group consisting of n, 0 <w ≦ 0.6, 0.4 ≦ a ≦ 0.8, 0.1 ≦ b
≦ 0.4, 0 ≦ x ≦ 0.3, 0.2 <y ≦ 0.5, 0.
8 ≦ z ≦ 1.3, and 1.7 ≦ (a + b + x + y + z)
/1.2≦2.2), and the main component of the alloy phase is C15
A hydrogen storage alloy that is a (MgCu ₂ ) type Lavas phase. 3. The hydrogen storage alloy according to claim 1, wherein y + z ≦ 1.5 in the general formula. 4. The hydrogen storage alloy according to claim 1, which has been subjected to a homogenizing heat treatment at 1000 to 1300 ° C. for at least 1 hour in a vacuum or an inert gas atmosphere. 5. A hydrogen storage alloy electrode comprising the hydrogen storage alloy according to claim 1 or a hydride thereof.