JPH06251769A - Hydrogen storage alloy electrode and manufacture thereof - Google Patents

Abstract

PURPOSE:To improve an initial discharge characteristic without spoiling high capacity by solving a problem that discharge capacity is very small in the initial stage of a charging and discharging cycle when conventional Zr-Mn- Mo-Cr-Ni type alloy is used in an electrode in a hydrogen storage alloy electrode to store and release electrochemical hydrogen reversibly. CONSTITUTION:A general equation of hydrogen storage alloy or the hydride is expressed by ZrMnwMoxMyNiz [provided that, M is at least a single kind of element selected from a group composed of Fe and Co, and (0.4<=w<=0.8, 0.1<=x<=0.35, 0<=y<=0.2, 1.0<=z<=1.5 and 2.0<=w+x+y+z<=2.4) is realized]. A main component of an allay phase is a C15 type lavas phase, and the crystal lattice constant (a) is (7.04 angstrom<=a<=7.13 angstrom).

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 capable of reversibly electrochemically storing and releasing hydrogen and a method for producing the same.

[0002]

2. Description of the Related Art Lead batteries and alkaline batteries are widely used as storage batteries for various power sources. Among them, the alkaline battery has been used for various portable devices, and the large battery has been used for industrial purposes because it can be expected to have high reliability and can be made compact and lightweight. In this alkaline storage battery, an air electrode, a silver oxide electrode, and the like have been taken up as a positive electrode, but in most cases, it is a nickel electrode. Nickel electrode has improved characteristics instead of the pocket type instead of the sintered type, and has become possible to be hermetically sealed and expanded its applications. On the other hand, as the negative electrode, in addition to cadmium, zinc, iron, hydrogen, etc. are targeted, but at the present time, the cadmium electrode is mainly used. However, a nickel-hydrogen storage battery using a metal hydride, that is, a hydrogen storage alloy, as a negative electrode has attracted attention in order to achieve a higher energy density, and many proposals have been made for a manufacturing method and the like.
The hydrogen storage alloy electrode of an alkaline storage battery, which uses a hydrogen storage alloy capable of reversibly absorbing and releasing hydrogen for the negative electrode, has a theoretical capacity density larger than that of the cadmium electrode and does not have deformation such as zinc electrode or dendrite formation. Therefore, it is expected as a negative electrode for an alkaline storage battery that has a long life, is pollution-free, and has a high energy density.

As an alloy used for such a hydrogen storage alloy electrode, generally, a Ti-Ni-based and La (or Mm) -Ni-based multi-component alloy is well known. Ti
-Ni-based multi-component alloys are AB type (A: La, Z
Elements with a high affinity for hydrogen, such as r and Ti, B: N
i, Mn, Cr and other transition elements)
This type characteristically exhibits a relatively large discharge capacity early in the charge / discharge cycle. However, when charging and discharging are repeated, it is difficult to maintain the capacity for a long time. Also, AB ₅ type La (or M
The m) -Ni-based multi-component alloy has been extensively developed in recent years as an electrode material, and in particular, the Mm-Ni-based multi-component alloy has already been put into practical use, but this alloy also has a relatively small discharge capacity. It has problems such as insufficient life performance as a battery electrode and high material cost. Therefore,
Further, a new 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 having a high capacity and a long life. As for this alloy system, for example, ZrMoαNiβ system alloy (JP-A-64-48370), AxByNiz system alloy (JP-A-1-102855), ZrαMnβ.
MoγCrδNiε (Japanese Patent Laid-Open No. 4-63240) and the like have been proposed.

[0004]

However, AB ₂
When a type Lavas phase alloy is used for the electrode, Ti-N
Although the discharge capacity is large and the life can be extended as compared with the i-based or La (or Mm) -Ni-based multi-component alloy, further improvement in performance is desired. And the alloy system is Z
By limiting the composition to the r-Mn-Mo-Cr-Ni system and adjusting the composition, a hydrogen storage alloy electrode having a discharge capacity of about 0.35 Ah / g was obtained (JP-A-4-63240). Furthermore, by increasing the amount of Mn and limiting the amount of Cr, the homogeneity of the alloy is improved and the discharge capacity is further increased.

Such Zr-Mn-Mo-Cr-Ni
Although the hydrogen-storing alloy-based electrode has a high capacity, it has a problem that the discharge capacity at the beginning of the charge / discharge cycle is very small. The present invention is to solve the above conventional problems,
An object of the present invention is to provide a hydrogen storage alloy electrode which can improve initial discharge characteristics without impairing high capacity by improving the hydrogen storage alloy.

[0006]

In order to achieve the above object, the present invention has a general formula of ZrMn _w Mo _x M _y Ni _z (where M is at least one selected from the group consisting of Fe and Co). Element, 0.4 ≦ w ≦ 0.8, 0.1 ≦
x ≦ 0.35, 0 ≦ y ≦ 0.2, 1.0 ≦ z ≦ 1.5,
And 2.0 ≦ w + x + y + z ≦ 2.4), and the main component of the alloy phase is C15 (MgCu ₂ ) type Lavas (Lav).
es) phase, and its crystal lattice constant (a) is 7.
A hydrogen storage alloy or a hydride thereof having a thickness of 04 Å ≦ a ≦ 7.13 Å is used.

[0007]

The hydrogen storage alloy electrode of the present invention is the same as the conventional Zr-M
It is an improvement of the n-Mo-Cr-Ni-based Larvus phase alloy. That is, the conventional alloy has a C content in an alkaline solution.
Since the passive film of r is formed, it is difficult to electrochemically store and release hydrogen at the beginning of the charge and discharge cycle. In the present invention, Cr of the composition of the conventional alloy is changed to M (M is Fe
And at least one element selected from the group consisting of Co), which improves the activity for electrochemical hydrogen absorption / desorption, and efficiently produces a large amount of hydrogen from the beginning of the charge / discharge cycle. It can be occluded and released. Therefore, an alkaline storage battery constituted by using the electrode of the present invention, for example, a nickel-hydrogen storage battery can have excellent initial discharge characteristics without impairing the high capacity as compared with the conventional storage battery of this type.

Next, the range of each composition is determined mainly from the viewpoint of securing the hydrogen storage-release amount. Mo is hydrogen storage
Ni contributes to the increase in the release amount, and Ni causes a decrease in the storage-release amount, but contributes to the improvement of the electrochemical activity for hydrogen storage-release. However, when the Mo amount x is less than 0.1, the effect of Mo is small, and when the Mo amount x exceeds 0.35, the homogeneity of the alloy is extremely deteriorated, and conversely the hydrogen storage-release amount decreases. Further, when the Ni content z is larger than 1.5, the hydrogen equilibrium pressure increases, so the hydrogen storage-release quantity decreases, and when the Ni content z is less than 1.0, the electrochemical activity for hydrogen storage-release is decreased. Is not obtained and the discharge capacity becomes small. Therefore, it is suitable that the Mo amount x and the Ni amount z are 0.1 ≦ x ≦ 0.35 and 1.0 ≦ z ≦ 1.5, respectively. However, since Mo and Ni have opposite effects,
The balance between the Mo amount x and the Ni amount z is important, and if z−x is 1.2 or less, the hydrogen storage-release amount becomes particularly large. Therefore, x and z are within the above range, and z-
It is desirable that x ≦ 1.2.

M also contributes to the further improvement of the activity for electrochemical hydrogen storage-release. However, when the M amount y exceeds 0.2, the hydrogen storage-release capacity of the alloy is affected and the hydrogen storage-release amount becomes small. Also, when y = 0,
That is, even when Cr is removed from the conventional alloy composition, the electrochemical activity for hydrogen storage-release is improved. Therefore, 0 ≦ y ≦ 0.2 is appropriate for the M amount y. Above all, when the M amount y is smaller than the Mo amount x, the hydrogen equilibrium pressure becomes low and the discharge capacity becomes particularly large. Therefore, it is desirable that the amount of M be 0 ≦ y ≦ 0.2 and y ≦ x. Mn affects the flatness of the hydrogen equilibrium pressure in the P (hydrogen pressure) C (composition) T (temperature) curve, and when the Mn amount w is 0.4 or more, the flatness is improved and the discharge capacity is increased. . However, when the Mn amount w exceeds 0.8, Mn is apt to be eluted into the electrolytic solution and the cycle life characteristics deteriorate. Therefore, 0.4 ≦ w ≦ 0.8 is appropriate for the Mn amount w.

In the hydrogen storage alloy of the present invention, the homogeneity and crystallinity of the alloy are improved by carrying out a homogenizing heat treatment after the alloy is produced, so that the discharge capacity becomes particularly large. But,
If the heat treatment temperature is lower than 1000 ° C., the heat treatment has no effect, and if the heat treatment temperature is higher than 1300 ° 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, it is desirable to carry out a homogenizing heat treatment for at least 1 hour in a vacuum at 1000 to 1300 ° C. or in an inert gas atmosphere after alloy production.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. Commercially available Zr, Mn, Mo, Fe, Co, N
Alloys having the compositions shown in Tables 1 and 2 were prepared by heating and melting an i metal as a raw material in an arc melting furnace in an argon atmosphere. However, the Mn amount w is 0.8
The above materials were produced in an induction heating furnace because a large amount of Mn evaporates and it is difficult to obtain the target alloy when produced in an arc furnace. Next, homogenization heat treatment was performed at 1100 ° C. for 12 hours in vacuum to obtain an alloy sample. In addition, the sample No. For 1 and 2, Fe or C of the above metals
Cr was used instead of o.

[0012]

[Table 1]

[0013]

[Table 2]

A part of these alloy samples is used for alloy analysis such as X-ray diffraction and hydrogen absorption-desorption amount measurement (normal P-C-T measurement) in a hydrogen gas atmosphere, and the rest is used for electrode characteristic evaluation. I was there. Sample No. Sample Nos. 1 to 7 are comparative examples having different constituent elements or alloy compositions from the present invention. 8
33 are some examples of the hydrogen storage alloy of the present invention. First, X-ray diffraction measurement was performed on each alloy sample.
As a result, it was confirmed that the main component of the alloy phase in all the alloy samples was a C15 type Larvus phase (MgCu ₂ type face centered cubic structure). Further, the homogenized heat-treated alloy had a larger and sharper peak of the face-centered cubic structure than the one before the heat treatment.
It was found that the proportion of the type 5 Larvus phase was increased and the homogeneity and crystallinity of the alloy were also improved. Especially Mn amount w is 0.8
It was confirmed that the target alloys having a uniform composition were obtained from the above. Regarding the crystal lattice constant, Sample No. Three
Was less than 7.04 Å, but was 7.04 to 7.13 Å in all other cases. Sample No. With respect to the alloys 1 to 33, a unit cell test was conducted to evaluate electrode characteristics as an anode for an alkaline storage battery by electrochemical charging / discharging reaction, in particular, initial discharge characteristics.

Sample No. The alloys 1 to 33 were pulverized to have a particle size of 400 mesh or less, and 1 g of the alloy powder, 3 g of carbonyl nickel powder as a conductive agent and 0.12 g of polyethylene fine powder as a binder were sufficiently mixed and stirred, 24.5 mm in diameter and 2.5 by pressing
It was formed into a disk shape of mm. 1 at 130 ℃ in vacuum
It was heated for a period of time to melt the binder and form a hydrogen storage alloy electrode. A nickel wire lead was attached to the hydrogen storage alloy electrode to serve as a negative electrode, a sintered nickel electrode having an excessive capacity was used as a positive electrode, a polyamide nonwoven fabric was used as a separator, and a potassium hydroxide aqueous solution having a specific gravity of 1.30 was used as an electrolytic solution. At 25 ° C., charging and discharging were repeated at a constant current, and the discharge capacity of the negative electrode was measured in each cycle. The amount of electricity charged is 100 mA x 1 g of hydrogen storage alloy.
It was 5 hours, and the discharge was similarly performed at 50 mA / g, and cut at 0.8V. The results are shown in FIG. 1 and FIG.
Shown in. 1 and 2, the horizontal axis represents the number of charge / discharge cycles, and the vertical axis represents the discharge capacity per 1 g of the alloy. The numbers in the figures are the sample No. of Table 1 or Table 2. Is consistent with

From FIG. 1 and FIG. 2, the sample No. 1 and 2
In (Comparative example), the discharge capacity in the first cycle is 10 to 20 m
Ah / g was 10 to 50 mAh / g in the second cycle, which became almost constant after 10 cycles, whereas when the hydrogen storage alloys of the examples of the present invention were used, the first cycle was 200 to 250 mAh. / G, the second cycle is 2
80 to 320 mAh / g, which was almost constant after 3 cycles and was 340 to 380 mAh / g, and it was found that the initial discharge characteristics were greatly improved as compared with the conventional case. Also, 50
When the unit cell test was conducted continuously until the cycle, sample N
o. 3 to 6 (comparative examples) have a small hydrogen storage capacity,
In addition, the sample No. 7 (Comparative Example) has poor activity for electrochemical hydrogen absorption-desorption, and thus each of 200-200
The saturation capacity was 280 mAh / g, which was small. In addition, the sample No. In Comparative Example 1 (Comparative Example), the amount of Mn was large, so that Mn was severely eluted into the alkaline electrolyte, and the discharge capacity greatly decreased as the charge and discharge cycle was repeated. For these samples No. It was found that in the hydrogen storage alloy electrodes of Examples 8 to 33 of the present invention, the saturation capacity was as large as 340 to 380 mAh / g, and the decrease in discharge capacity with charge / discharge cycles was very small.

Further, a sealed nickel-hydrogen storage battery was manufactured by using the above hydrogen storage alloy by the following method. Sample N from the alloys shown in Table 1 or Table 2
o. 1, 2, 12, 16, 21, 26, 29 and 33
8 kinds of alloys are selected, and each hydrogen storage alloy made into powder of 400 mesh or less is mixed and stirred with a dilute aqueous solution of carboxymethyl cellulose (CMC) to form a paste, and an average pore size of 150 μm as an electrode support,
It was filled in a foamed nickel sheet having a porosity of 95% and a thickness of 1.0 mm. This was dried at 120 ° C., pressed by a roller press, and the surface thereof was coated with a fluororesin powder to obtain a hydrogen storage alloy electrode. The electrodes were adjusted to have a width of 3.3 cm, a length of 21 cm, and a thickness of 0.40 mm, and lead plates were attached at two predetermined positions. Then, in combination with the positive electrode and the separator, the three layers were spirally wound and housed in an SC size battery case. At this time, a known foaming nickel electrode was selected as the positive electrode, and the width was 3.3 cm and the length was 1 cm.
It was used as 8 cm. Also in this case, the lead plates were attached at two positions. The separator is made of hydrophilic polypropylene non-woven fabric, and the electrolyte has a specific gravity of 1.2.
0 g of potassium hydroxide aqueous solution containing 30 g of lithium hydroxide /
1 The dissolved product was used. This was sealed to form a sealed battery. This battery has a positive electrode capacity regulation and a theoretical capacity of 3.0
It was Ah.

The battery thus manufactured was evaluated by a usual charge / discharge cycle test. That is, charging is 0.5C (2-hour rate) up to 150%, discharging is 0.2C.
The final voltage was set to 1.0 V (at a rate of 5 hours), and the charge / discharge cycle was repeated at 20 ° C. As a result, the sample No. 1
It took 10 to 15 cycles to reach the theoretical capacity in Examples 2 and 2, but other than that, all the cells reached the theoretical capacity of 3.0 Ah in 3 to 5 cycles of charging and discharging, and then maintained stable battery performance. .

[0019]

As is apparent from the above examples, the hydrogen storage alloy electrode of the present invention can be electrochemically occluded by substituting M for Cr in the alloy composition of the conventional hydrogen storage alloy electrode. The activity for release is increased, and a large amount of hydrogen can be efficiently absorbed and released from the beginning of the charge / discharge cycle. Therefore, the alkaline storage battery using this as a negative electrode can have excellent initial discharge characteristics without impairing the high capacity as compared with the conventional storage battery of this type.

[Brief description of drawings]

FIG. 1 is a charge / discharge cycle characteristic diagram showing the results of a unit cell test using an example of the present invention and a conventional hydrogen storage alloy electrode.

FIG. 2 is a charge / discharge cycle characteristic diagram showing the results of a single cell test using the hydrogen storage alloy electrode of the example of the present invention.

Continuation of the front page (51) Int.Cl. ⁵ Identification number Reference number in the agency FI Technical indication location H01M 4/26 J 8520-4K (72) Inventor Naoko Maekawa 1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric Industrial Co., Ltd. (72) Inventor Tsutomu Iwaki, 1006 Kadoma, Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (3)

[Claims] 1. The general formula is ZrMn _w Mo _x M _y Ni _z (wherein M is at least one element selected from the group consisting of Fe and Co, and 0.4 ≦ w ≦ 0.8, 0.1 ≦
x ≦ 0.35, 0 ≦ y ≦ 0.2, 1.0 ≦ z ≦ 1.5,
And 2.0 ≦ w + x + y + z ≦ 2.4), the main component of the alloy phase is a C15 type Lavas phase, and the crystal lattice constant (a) is 7.04 Å ≦ a ≦ 7.13 Å. A hydrogen storage alloy electrode characterized by using a hydrogen storage alloy or a hydride thereof. 2. The hydrogen storage alloy electrode according to claim 1, wherein y ≦ x and z−x ≦ 1.2. 3. The general formula is ZrMn _w Mo _x M _y Ni _z (wherein M is at least one element selected from the group consisting of Fe and Co, 0.4 ≦ w ≦ 0.8, 0.1 ≦
x ≦ 0.35, 0 ≦ y ≦ 0.2, 1.0 ≦ z ≦ 1.5,
And 2.0 ≦ w + x + y + z ≦ 2.4), the main component of the alloy phase is a C15 type Lavas phase, and the crystal lattice constant (a) is 7.04 Å ≦ a ≦ 7.13 Å. After producing a hydrogen storage alloy that is
A method for producing a hydrogen storage alloy electrode, comprising a step of performing homogenizing heat treatment for at least 1 hour in a vacuum at 1300 ° C. or in an inert gas atmosphere.