JPH0582125A - Hydrogen occluding alloy electrode - Google Patents

Abstract

PURPOSE:To provide a hydrogen occluding alloy electrode by which an initial discharging characteristic can be improved without damaging a high capacity by solving a problem such as the discharging characteristic is extremely bad in the initial stage of a charging/discharging cycle in the case where a conventional Zr-Mn-V-Cr-Ni type alloy is used as an electrode in an AB2 type Laves phase hydrogen occluding alloy electrode by which electrochemical hydrogen occlusion/release can be carried out reversibly. CONSTITUTION:A hydrogen occluding alloy electrode is formed of hydrogen occluding alloy or its hydride on which a general equation is expressed by ZrMnwVxMyNiz(provided that, M is one or more kinds of elements selected from Fe and Co, 0.4<=w<=0.8, 0.1<=x<=0.3, 0<y<=0.2, 1.2<=z<=1.5 and also 2.0<=w+x+y+z<=2.4), and in which a main component of a alloy phase is a C15(MgCu2) type Laves phase, and in which its crystal lattice contant (a) is 7.03A<=(a)<=7.10A.

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.

[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 storage battery can be expected to have high reliability and can be made compact and lightweight. For this reason, the small battery has been used for various portable devices and the large battery for industrial use.

In this alkaline storage battery, an air electrode, a silver oxide electrode, etc. are also taken up as a positive electrode,
In most cases it is a nickel pole. The characteristics have been improved from the pocket type to the sintered type, and it has become possible to further seal and expand the applications.

On the other hand, as the negative electrode, zinc, iron, hydrogen, etc. are targeted in addition to cadmium, but at present, the main component is a cadmium electrode. However, a nickel-hydrogen storage battery using a metal hydride, that is, a hydrogen storage alloy electrode, has been attracting attention in order to achieve a higher energy density, and many proposals have been made for a manufacturing method and the like.

A hydrogen storage alloy electrode of an alkaline storage battery, which uses a hydrogen storage alloy capable of reversibly absorbing and releasing hydrogen as a negative electrode, has a theoretical capacity density larger than that of a cadmium electrode and causes deformation such as a zinc electrode and formation of dendrite. Therefore, it is expected as a negative electrode for alkaline storage batteries that has a long life, is pollution-free, and has a high energy density.

As alloys used for such hydrogen storage alloy electrodes, generally, Ti-Ni-based and La (or Mm) -Ni-based multi-component alloys are well known. T
i-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 feature shows 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 charge / discharge is repeated. Also,
AB ₅ type La (or Mm) -Ni-based multi-component alloys have been extensively developed in recent years as electrode materials, and in particular, Mm-Ni-based multi-component alloys have already been put to practical use. 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, AB ₂ type Laves
The phase alloy has a relatively high hydrogen storage capacity and is promising as an electrode having a high capacity and a long life. Already for this alloy system,
For example, ZrαVβNiγMδ type alloy (Japanese Patent Laid-Open No. 64-60)
961) and AxByNiz alloys (JP-A-1-1-1).
No. 02855), ZrαMnβVγCrδNiε.
(Japanese Patent Laid-Open No. 3-2899041) is proposed.

[0008]

However, AB ₂
When a type Laves phase alloy is used for the electrode, Ti-
Although the discharge capacity is higher and the life can be extended as compared with the Ni-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-V-Cr-Ni system and adjusting the composition, a hydrogen storage alloy electrode having a discharge capacity of 0.34 Ah / g or more was obtained (JP-A-3-289041, etc.). Such a Zr-Mn-V-Cr-Ni-based hydrogen storage alloy electrode has a high capacity, but there is a problem that the discharge characteristics at the beginning of the charge / discharge cycle are very poor.

The present invention solves the above-mentioned conventional problems, and it is an object of the present invention to provide a hydrogen storage alloy electrode by improving the hydrogen storage alloy, which can improve the initial discharge characteristics without impairing the high capacity. To aim.

[0010]

Means for Solving the Problems The present invention to achieve the above object, the general _{formula, ZrMn w V x M y Ni} z ( however, M is Fe, 1 or more selected from among Co Element, 0.4 ≦ w ≦ 0.8, 0.1 ≦ x ≦ 0.3, 0 <
y ≦ 0.2, 1.2 ≦ z ≦ 1.5, and 2.0 ≦ w + x
+ Y + z ≦ 2.4), and the main component of the alloy phase is C15.
Type Laves phase, and its crystal lattice constant a is
A hydrogen storage alloy having a hydrogen content of 7.03Å ≦ a ≦ 7.10Å or a hydride thereof is used.

[0011]

The hydrogen storage alloy electrode of the present invention is the same as the conventional Zr-M
This is an improvement of the n-V-Cr-Ni-based Laves phase alloy. According to the present invention, Cr of the composition of the conventional alloy is M (M
Is substituted with one or more elements selected from Fe and Co), so that the electrochemical activity for hydrogen storage-release is increased, so that a large amount of hydrogen can be efficiently generated from the initial stage in charge and discharge characteristics. It can be occluded and released.

Therefore, an alkaline storage battery constructed 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 battery of this type. Become.

[0013]

An embodiment of the present invention will be described below with reference to the drawings. Commercially available Zr, Mn, V, Fe, Co, Ni
An alloy having a composition as shown in (Table 1) and (Table 2) was prepared by heating and melting a metal as a raw material in an arc melting furnace in an argon atmosphere. However, when the Mn amount w is 0.8 or more, a large amount of Mn is evaporated 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. Then, heat treatment was performed in vacuum at 1100 ° C. for 12 hours to obtain an alloy sample. In addition, the sample No. in (Table 1). For 1 and 2, Fe or C of the above metals
Cr was used instead of o.

[0014]

[Table 1]

[0015]

[Table 2]

A part of this alloy sample is used for alloy analysis such as X-ray diffraction and hydrogen absorption-desorption amount measurement (normal P (hydrogen pressure) -C (composition) -T (temperature) measurement) in a hydrogen gas atmosphere. The rest was used for electrode characteristic evaluation.

Sample No. Sample Nos. 1 to 6 are comparative examples having different constituent elements or alloy compositions from the present invention. 7-31
Are several examples of hydrogen storage alloys of the present invention. First, X-ray diffraction measurement was performed on each alloy sample. As a result, the main component of the alloy phase was C1 in all the alloy samples.
It was confirmed to be a 5 type Laves phase (MgCu ₂ type fcc structure). Further, since the fcc peak was larger and sharper than that before the heat treatment, it was found that the heat treatment increased the proportion of the C15 type Laves phase and improved the homogeneity and crystallinity of the alloy. In particular, it was confirmed that the target alloy having a uniform composition was obtained even when the Mn content w was 0.8 or more. For the crystal lattice constant, see Sample N
o. 3 was smaller than 7.03Å, but other than that, all were 7.04 to 7.08Å.

Sample No. With respect to the alloys Nos. 1 to 31, a single cell test was performed to evaluate the electrode characteristics as a negative electrode for an alkaline storage battery by an electrochemical charge / discharge reaction, particularly the initial discharge characteristics.

Sample No. The alloys Nos. 1 to 31 were pulverized to have a particle size of 400 mesh or less, and 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. Then, it was formed into a disk shape of 24.5Φ × 2.5 mmH by press working. This was heated in vacuum at 130 ° C. for 1 hour to melt the binder and form a hydrogen storage alloy electrode.

A nickel wire lead is attached to the hydrogen storage alloy electrode to serve as a negative electrode, a sintered nickel electrode having an excessive capacity as a positive electrode, a polyamide nonwoven fabric as a separator, and an aqueous potassium hydroxide solution having a specific gravity of 1.30. As an electrolytic solution, charging and discharging were repeated at a constant current at 25 ° C., and the discharge capacity in each cycle was measured. In addition,
The amount of charge electricity is 100 mA / g of hydrogen storage alloy × 5 hours, and the discharge is similarly performed at 50 mA / g,
It was cut at 0.8V. The results are shown in FIGS. 1 and 2. 1 and 2 show the number of charge / discharge cycles on the horizontal axis and the discharge capacity per 1 g of alloy on the vertical axis, and the numbers in the figures are the sample numbers of (Table 1) or (Table 2). ．
Is consistent with 1 and 2, the sample No. In 1 and 2, the discharge capacity in the first cycle was 0.01 to 0.02.
Ah / g, the second cycle is 0.01 to 0.05 Ah / g
While it became almost constant after 10 cycles, when the hydrogen storage alloy of the present invention was used, both were 0.2 to 0.25 Ah / g in the first cycle and 0.27 to 0.27 in the second cycle. It was found that 0.3 Ah / g was substantially constant after 3 cycles and was 0.34 to 0.37 Ah / g, and the initial discharge characteristics were greatly improved as compared with the conventional case.

Further, when the unit cell test was continuously conducted up to 50 cycles, the sample No. Samples Nos. 3 to 6 had small hydrogen storage capacity of 0.23 to 0.28 Ah / g and thus had a small saturation capacity. No. 1 had a large amount of Mn, so that Mn was severely eluted into the alkaline electrolyte, and the discharge capacity greatly decreased as the charge and discharge cycle was repeated. On the other hand, the hydrogen storage alloy electrode of the present invention has a saturation capacity of 0.34 to 0.3.
It was found to be as large as 6 Ah / 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.

From the alloys shown in (Table 1) or (Table 2), sample No. 1,7,2,12,16,24,30 and 31 alloys are selected, and each hydrogen storage alloy made into powder of 400 mesh or less is mixed with a dilute aqueous solution of carboxymethyl cellulose (CMC) and stirred to form a paste. Then, a foamed nickel sheet having an average pore size of 150 μm, a porosity of 95% and a thickness of 1.0 mm was filled as an electrode support. 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.

Each of these electrodes has a width of 3.3 cm and a length of 2
The lead plate was adjusted to 1 cm and the thickness was 0.40 mm, and the lead plates were attached to two predetermined places. Then, in combination with the positive electrode and the separator, the three layers were made into a cylindrical shape and housed in an SC size battery case. A known foaming nickel electrode was selected as the positive electrode at this time and used with a width of 3.3 cm and a length of 18 cm. Also in this case, the lead plates were attached at two places. Also,
As the separator, a polypropylene non-woven fabric having hydrophilicity was used, and as the electrolytic solution, 30 g / l of lithium hydroxide was dissolved in an aqueous potassium hydroxide solution having a specific gravity of 1.20. This was sealed to form a sealed battery. This battery has a positive electrode capacity regulation and a theoretical capacity of 3.0 Ah.

The battery thus produced was evaluated by a usual charge / discharge cycle test. That is, charging is 0.5C (2-hour rate) up to 150% and discharging is 0.2C.
The final voltage was 1.0 V at (5 hour rate), 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 batteries reached the theoretical capacity of 3.0 Ah in 3 to 5 cycles of charging and discharging, and then maintained stable battery performance. ..

Here, the function of the alloy composition of the present invention will be described. Since the conventional Zr-Mn-V-Cr-Ni alloy forms a passive film of Cr in an alkaline solution, it has been difficult to electrochemically store and release hydrogen at the initial stage of charge and discharge cycles. Therefore, the Cr of the conventional alloy composition is M
By substituting (M is one or more elements selected from Fe and Co), the activity for electrochemical hydrogen storage-release is improved, and a large amount of hydrogen is efficiently produced from the beginning of the charge / discharge cycle. It can be occluded and released.

Next, the range of each composition is mainly for ensuring the hydrogen storage-release amount. V contributes to an increase in hydrogen storage-release amount, and Ni causes a decrease in storage-release amount, but contributes to improvement of electrochemical activity for hydrogen storage-release. However, if the V amount x is smaller than 0.1, the effect of V is small, and if the V amount x exceeds 0.3, the homogeneity of the alloy is deteriorated and conversely the hydrogen storage-release amount is reduced. Also, N
When the i amount z is larger than 1.5, the hydrogen equilibrium pressure increases and the hydrogen storage-release amount decreases. Therefore, the V amount x and the Ni amount z are 0.1 ≦ x ≦ 0.3 and 1.2 ≦ z, respectively.
≦ 1.5 is suitable. However, since V and Ni exert contradictory effects, it is important to balance the V amount x and the Ni amount z. Even if x and z are within the above range, z−x
When the ratio exceeds 1.2, the hydrogen storage-release amount becomes small. Therefore, x and z are within the above range, and z-
It is necessary that x ≦ 1.2.

M (M is one or more elements selected from Fe or Co) also contributes to the further improvement of the electrochemical activity for 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. Therefore, M amount y
Is suitable for 0 <y ≦ 0.2, but if it is more than V amount x, the hydrogen equilibrium pressure rises and the discharge capacity becomes small. Therefore, regarding the amount of M, it is necessary that 0 <y ≦ 0.2 and y ≦ x.

Mn affects the flatness of the hydrogen equilibrium pressure in the PCT curve, and when the amount of Mn is 0.4 or more, the flatness becomes very good and the discharge capacity increases. But M
If the amount of n exceeds 0.8, Mn will be much eluted into the electrolytic solution and the cycle life characteristics will be deteriorated. Therefore, Mn
A suitable amount is 0.4 ≦ w ≦ 0.8.

From the above, it is understood that it is important to satisfy the conditions of the alloy composition of the present invention in order to obtain a hydrogen storage alloy electrode having a high capacity and excellent initial discharge characteristics.

[0031]

EFFECTS OF THE INVENTION The hydrogen storage alloy electrode is electrochemically produced by substituting Cr (M is one or more elements selected from Fe and Co) in the alloy composition of the conventional hydrogen storage alloy electrode. Since a large amount of hydrogen storage-release activity is increased, a large amount of hydrogen can be stored and released efficiently from the beginning of the charge / discharge cycle. Therefore, the alkaline storage battery having this as a negative electrode has excellent initial discharge characteristics without impairing the high capacity as compared with the conventional 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 (72) Inventor Yoshio Moriwaki 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Tsutomu Iwashiro 1006 Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd.

Claims (3)

[Claims] 1. A general _{formula, ZrMn w V x M y Ni} z ( however, M is Fe, at least one element selected from among Co, 0.4 ≦ w ≦ 0.8,0 1 ≦ x ≦ 0.3, 0 <
y ≦ 0.2, 1.2 ≦ z ≦ 1.5, and 2.0 ≦ w + x
+ Y + z ≦ 2.4), and the main component of the alloy phase is C15.
A hydrogen storage alloy electrode comprising a (MgCu ₂ ) -type Laves phase and having a crystal lattice constant (a) of 7.03Å ≦ a ≦ 7.10Å or a hydride thereof. 2. The hydrogen storage alloy electrode according to claim 1, wherein y ≦ x and z−x ≦ 1.2. 3. The hydrogen storage alloy electrode according to claim 1, wherein an alloy which has been subjected to homogenizing heat treatment in a vacuum at 1000 to 1300 ° C. or in an inert gas atmosphere after the alloy is produced is used.