JPH05343054A - Hydrogen storage alloy electrode - Google Patents

Abstract

PURPOSE:To improve a preservation characteristic at high temperature without detracting high capacity and an initial stage discharge characteristic, by solving a problem that a preservation at 65 deg.C is very inferior when sealed battery is made by utilizing Zr-Mn-V-M-Ni system Laves phase hydrogen storage alloy electrode. CONSTITUTION:This electrode is composed of hydrogen storage alloy or its hydride, of which a general formula is shown by ZrMnvVwMxWyNiz, (wherein, M is one kind or more of elements selected from Fe and Co, and 0.4<=v<=0.8, 0.1<=w<=0.3, 0<x<=0.2, 0<y<=0.1, 1.0<=z<=1.5 and 2.0<=v+w+x+y+z<=2.4); and the main component of an 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 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, in order to achieve a higher energy density, a nickel-hydrogen storage battery using a metal hydride, that is, a hydrogen storage alloy electrode has attracted attention, and many proposals have been made for its manufacturing method.

The 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 also causes deformation such as a zinc electrode and formation of dendrite. Since it does not exist, it is expected to be 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 a hydrogen storage alloy electrode, generally, Ti-Ni-based and La (or Mn) -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, W, and other transition elements), which has a relatively large discharge capacity at the beginning of the charging / discharging cycle, but it is difficult to maintain the capacity for a long time after repeated charging / discharging. There is a problem. Also, A
B ₅ type La (or Mn) -Ni-based multi-component alloys have been developed a lot as an electrode material in recent years.
Although the Mn-Ni-based multi-component alloy has already been put into practical use, this alloy-based alloy also has problems such as a relatively small discharge capacity, insufficient life performance as a battery electrode, and high material cost. Have 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) is proposed. Also, an alloy with improved discharge characteristics at the beginning of the charge / discharge cycle (Japanese Patent Application No. 3-6
6354, Japanese Patent Application No. 3-66355, Japanese Patent Application No. 3-66
No. 358 and Japanese Patent Application No. 3-66359).

[0008]

However, when an AB ₂ type Laves phase alloy is used for the electrode, Ti-
Although the discharge capacity is larger than that of the Ni-based or La (or Mn) -Ni-based multi-component alloy, there is a problem that the discharge characteristics at the beginning of the charge / discharge cycle are very poor. So Zr-
By adjusting the composition with an Mn-VM-Ni-based alloy (M is one or more elements selected from Fe and Co),
It was possible to improve the initial discharge characteristics while maintaining a high capacity. However, when a sealed battery is used, the alloy composition elutes violently into the alkaline electrolyte, and the eluted elements are deposited in the form of conductive oxides, which causes a short circuit. There is a problem that the voltage drops.

The present invention has been made to solve the above-mentioned conventional problems. By improving the hydrogen storage alloy, a hydrogen storage alloy electrode having improved high temperature storage characteristics without impairing high capacity and excellent initial discharge characteristics is provided. The purpose is to provide.

[0010]

SUMMARY OF THE INVENTION The present invention, in order to achieve the above object, the general formula _{ZrMn v V w M x W y} Ni z ( however, M is Fe, 1 or more selected from among Co Element of 0.4 ≦ v ≦ 0.8, 0.1 ≦ w ≦ 0.3, 0 <
x ≦ 0.2, 0 <y ≦ 0.1, 1.0 ≦ z ≦ 1.5,
2.0 ≦ v + w + x + y + z ≦ 2.4), and a hydrogen storage alloy or a hydride thereof whose main component of the alloy phase is a C15 (MgCu ₂ ) type Laves phase is used.

[0011]

Therefore, according to the present invention, the conventional Zr--Mn
Compared with the -VM-Ni-based Laves phase alloy, by adding an appropriate amount of W to the conventional alloy, the elution of the alloy composition into the alkaline electrolyte can be suppressed, and in addition, in terms of electrochemical charge / discharge characteristics. A large amount of hydrogen can be efficiently absorbed and released from the initial stage.

Therefore, an alkaline storage battery constituted by using the hydrogen storage alloy electrode of the present invention, for example, a nickel-hydrogen storage battery, has a high temperature storage characteristic without impairing the high capacity and the excellent initial discharge characteristic as compared with the conventional battery of this type. It will be possible to improve.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A specific embodiment of the present invention will be described below with reference to the drawings.

Example 1 Commercially available Zr, Mn, V, C
o, W, Ni metal as raw material in argon atmosphere
Z shown in (Table 1) by heating and melting in a melting furnace
rMn_0.6V_0.2Co _0.1W_yNi_1.2Alloy (y is 0.01
~ 0.3) was prepared. Then in vacuum at 1100 ° C for 1
It heat-processed for 2 hours and it was set as the alloy sample.

[0015]

[Table 1]

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. No. 1 is a conventional alloy and is a comparative example in which W is not added. Sample No. 5 to 7 are comparative examples in which the W amount y is larger than the claims of the present invention. 2 to 4 are the first embodiment of the hydrogen storage alloy electrode of the present invention. First, X-ray diffraction measurement was performed on each alloy sample. As a result, in all the alloy samples, the main component of the alloy phase was the C15 type Laves phase (MgCu ₂ type fc
c structure) was confirmed. Further, after the vacuum heat treatment, the fcc peak was larger and sharper than that before the heat treatment.
It was found that the proportion of s phase was increased and the homogeneity and crystallinity of the alloy were also improved. The crystal lattice constant decreased as the W amount y increased.
It was 7.07Å.

Next, for each alloy sample, P at 70 ° C.
CT measurement was performed. The hydrogenation characteristics were almost the same for all the alloy samples, but the hydrogen storage amount slightly decreased when the W amount y exceeded 0.1. Further, the vacuum heat treatment improved the flatness of the plateau region as compared with that before heat treatment, and increased hydrogen storage.

The above alloy samples 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, particularly the initial discharge characteristics.

Sample No. The alloys 1 to 7 were pulverized to have a particle size of 350 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, It was formed into a disk shape of 24.5Φ × 2.5 mmH by pressing. 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 was 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. The amount of electricity charged is 100 mA × 5.5 per 1 g of hydrogen storage alloy.
Time, the discharge is likewise carried out at 50 mA / g,
It was cut at 0.8V. The result is shown in FIG. FIG. 1 shows the number of charge / discharge cycles on the horizontal axis and the discharge capacity per 1 g of alloy on the vertical axis. The numbers in the figure are the sample No. of (Table 1). Is consistent with From FIG. 1, it can be seen that the initial discharge characteristics deteriorate as the W amount y increases. However, the discharge capacity at the first cycle was the sample No. In Samples Nos. 5 to 7, the W content was 50% or less compared to the case where W was not added (Sample No. 1). In Nos. 2 to 4, it was about 70% of the case where W was not added, and it was found that the deterioration of the initial discharge characteristics was not so large.

Further, a sealed nickel-hydrogen storage battery was manufactured by using the above hydrogen storage alloy electrodes by the following method.

Each hydrogen storage alloy made into powder of 350 mesh or less is carboxymethyl cellulose (CM).
The mixture was mixed with the dilute aqueous solution of C) and stirred to form a paste, and the electrode support had an average pore size of 150 μm and a porosity of 95.
%, And a foamed nickel sheet having a thickness of 1.0 mm was filled.
This was vacuum dried at 130 ° C., pressed by a roller press, and the surface thereof was coated with fluororesin powder to obtain a hydrogen storage alloy electrode.

Each of these electrodes has a width of 3.3 cm and a length of 21
The thickness was adjusted to cm and the thickness was 0.40 mm, and the lead plates were attached at two predetermined places. Then, in combination with the positive electrode and the separator, the three cylindrical layers were spirally formed and housed in an SC size battery case. As the positive electrode at this time, a known foaming nickel electrode was selected 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. As the separator, a polypropylene non-woven fabric having hydrophilicity was used, and as the electrolytic solution, 30 g / 1 of lithium hydroxide dissolved in an aqueous solution of potassium hydroxide having a specific gravity of 1.25 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 Ah.

The battery thus produced was charged and discharged at 20 ° C. with a charge of 0.5 C (2 hour rate) up to 150% and a discharge of 0.2 C (5 hour rate) with a final voltage of 1.0 V. Twenty cycles were carried out and then left at 65 ° C.
FIG. 2 shows each battery voltage with respect to the number of storage days. The numbers in the figure indicate the sample No. of (Table 1). Is consistent with Conventional alloy sample No. In No. 1, the battery voltage drastically dropped after 10 days of storage, while the sample N containing W was added.
o. It was found that in 2 to 7, the battery voltage drop was very small even after storage for 30 days.

From these results, the W amount y is 0.01 to 0.
It was found that, by carrying out No. 1, it was possible to obtain a hydrogen storage alloy electrode which did not contain W and which was excellent in high temperature storage characteristics while maintaining the discharge capacity and initial discharge characteristics of the hydrogen storage alloy electrode. This is because the addition of W suppresses the elution of the alloy composition into the alkaline electrolyte. But W in the alloy
Has the effect of lowering the initial electrochemical activity of the alloy, the initial discharge characteristics deteriorate as the amount of W added increases, but if the W amount y is 0.1 or less, It turns out that it doesn't have a big influence.

Example 2 Commercially available Zr, Mn, V, C
By using o, Fe, W, and Ni metals as raw materials and heating and melting in an arc melting furnace in an argon atmosphere, (Table 2)
ZrMn _v V _w M _x W with the W amount y shown in Table 3 set to 0.03
To prepare a _0.03 Ni _z alloy. However, the Mn amount v 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. Then, it was heat-treated in vacuum at 1100 ° C. for 12 hours to obtain an alloy sample.

[0028]

[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. 8 to 13 are comparative examples different from the present invention. 14 to 26 are the second embodiment 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 of all the alloy samples was the C15 type Laves phase (MgCu ₂ type fcc structure). Further, after the vacuum heat treatment, the fcc peak was larger and sharper than that before the heat treatment, so 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. It was Especially Mn amount v
It was also confirmed that the target alloys having a uniform composition were obtained for the alloys having a value of 0.8 or more. For the crystal lattice constant, sample N
o. 9 was smaller than 7.03Å, but all were 7.03 to 7.10Å excluding it.

Next, PCT measurement was performed at 70 ° C. for each alloy sample. Sample Nos. 9 and 13 have a large hydrogen equilibrium pressure, and Sample No. Nos. 10 and 12 had very poor plateau region flatness. Except for these, the hydrogenation characteristics of all alloy samples were not so different, and the hydrogen storage capacity was H / M = 1.0 to 1.2.
Sample No. 10-20% compared to 9, 10, 12, 13
I found it big. Further, the vacuum heat treatment improved the flatness of the plateau region as compared with that before the heat treatment and increased the hydrogen storage amount. This has the same tendency as in the case where W is not added, and it was confirmed that even if the W amount y was 0.03, the hydrogenation characteristics were almost the same as in the alloy without W added.

For the alloy samples as described above, a single cell test was conducted in the same manner as in Example 1 in order to evaluate the electrode characteristics of the negative electrode for alkaline storage batteries by the electrochemical charge / discharge reaction. The result is shown in FIG. FIG. 3 shows 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 figure are the sample numbers of (Table 2).
Is consistent with All the samples had excellent discharge characteristics at the beginning of the charge / discharge cycle, and no decrease in initial activity was observed even when W was added. However, sample No. 9, 10, 12,
Sample No. 13 has a small saturated discharge capacity because it has a small hydrogen storage capacity. In No. 8, since the amount of Ni was small, the electrochemical activity was poor and the initial discharge capacity and the saturation discharge capacity were small. In addition, sample No. Since No. 11 had a large amount of Mn, Mn was severely eluted into the alkaline electrolyte, and the discharge capacity was significantly reduced when the charge / discharge cycle was repeated. On the other hand, the hydrogen storage alloy electrode of the present invention showed a saturated discharge capacity of 0.34 to 0.37 Ah / g, and no decrease in capacity due to the addition of W was observed.

Further, a sealed nickel-hydrogen storage battery was prepared by using these hydrogen storage alloy electrodes in the same manner as in Example 1, and a storage test at 65 ° C. was conducted. The result is shown in FIG. FIG. 4 shows each battery voltage with respect to the number of days of storage, and the numbers in the figure indicate the sample No. of (Table 2). Is consistent with Sample No. 8, 11, 12 are 10 to 20 days
Battery voltage dropped drastically in the day. This is Mn
It seems that the amount of V and the amount of V are so large that the addition of W cannot suppress the elution into the alkaline electrolyte. However, it was found that the battery voltage drop was extremely small even after storage for 30 days except the above.

From the above single cell test results and 65 ° C. storage test results, it was found that the hydrogen storage alloy having the alloy composition of the present invention has a high capacity and excellent initial discharge characteristics. In the present embodiment, the alloy using Fe and Co as the M elements respectively has been described.
Almost the same results were obtained with the alloy containing both.

Here, the function of the alloy composition of the hydrogen storage alloy of the hydrogen storage alloy electrode of the present invention will be described. This alloy composition is for ensuring high capacity and excellent initial discharge characteristics.

V contributes to an increase in hydrogen absorption-desorption amount, and N
i causes a decrease in the amount of occlusion and release, but contributes to the improvement of the electrochemical activity for occlusion and release of hydrogen. However, when the V amount w is smaller than 0.1, the effect of V does not appear and 0.3
If it exceeds, the homogeneity of the alloy deteriorates and conversely the amount of occlusion-desorption decreases. Further, when the Ni content z is less than 1.0, the electrochemical activity is poor and the discharge capacity is small, and when it is more than 1.5, the hydrogen equilibrium pressure is high and the hydrogen absorption-desorption amount is reduced. Therefore, it is suitable that the V amount w and the Ni amount z are 0.1 ≦ w ≦ 0.3 and 1.0 ≦ z1.5, respectively.

M (M is one or more elements selected from Fe and Co) contributes to the electrochemical activity of the alloy. F
e and Co improve the electrochemical activity of the alloy, but M
If the amount x exceeds 0.2, the hydrogen storage-release capacity of the alloy is affected and the hydrogen storage-release amount becomes small. Therefore,
It is suitable that the M amount x be 0 <y ≦ 0.2.

Mn affects the flatness of the hydrogen equilibrium pressure in the PCT curve, and when the Mn amount is 0.4 or more, the flatness becomes very good and the discharge capacity increases. But Mn
If the amount exceeds 0.8, Mn is liable to be eluted into the electrolytic solution and the life characteristics are deteriorated. Therefore, the amount of Mn is 0.4 ≦
v ≦ 0.8 is suitable.

As described above, from the results of Example 1 and Example 2, in order to have good high-temperature storage characteristics without impairing high capacity and excellent initial discharge characteristics, the present invention was adopted as a hydrogen storage alloy electrode. It was found that it was necessary to satisfy the conditions of the alloy composition of.

[0040]

As is apparent from the above-mentioned embodiments, the hydrogen storage alloy electrode of the present invention has the conventional Zr-Mn-VM-Ni.
By adding an appropriate amount of W to the system Laves phase alloy (M is one or more elements selected from Fe and Co), the elution of the alloy composition into the alkaline electrolyte can be suppressed,
Moreover, since electrochemical charging / discharging characteristics can efficiently store and release a large amount of hydrogen from the beginning, alkaline storage batteries using this as an electrode have higher capacity and superior initial discharge than conventional batteries of this type. Good high temperature storage characteristics can be obtained without impairing the characteristics.

[Brief description of drawings]

FIG. 1 is a charge-discharge cycle characteristic diagram showing the results of unit cell tests in the first example and comparative example of the present invention.

FIG. 2 is a high temperature storage characteristic diagram showing the 65 ° C. storage test result.

FIG. 3 is a charge / discharge cycle characteristic diagram showing the results of unit cell tests in the second example and the comparative example of the present invention.

FIG. 4 is a high temperature storage characteristic diagram showing the results of the same 65 ° C. storage test.

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

Claims (2)

[Claims] 1. A general formula _{ZrMn v V w M x W y} Ni z ( however, M is Fe, at least one element selected from among Co, 0.4 ≦ v ≦ 0.8, 0.1 ≦ w ≦ 0.3,0
<X ≦ 0.2, 0 <y ≦ 0.1, 1.0 ≦ z ≦ 1.5,
2.0 ≦ v + w + x + y + z ≦ 2.4), and the hydrogen storage alloy electrode is characterized by using a hydrogen storage alloy having a C15 (MgCu ₂ ) type Laves phase as the main component of the alloy phase or a hydride thereof. 2. After producing the hydrogen storage alloy, 1000 to 130
The hydrogen storage alloy electrode according to claim 1, wherein the hydrogen storage alloy is subjected to a homogeneous heat treatment in a vacuum at 0 ° C or in an inert gas atmosphere.