JP3352479B2 - Hydrogen storage alloy electrode and method for producing the same - Google Patents

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 electrochemically storing and releasing hydrogen.

[0002]

2. Description of the Related Art Lead-acid batteries and alkaline batteries have been widely used as various power supplies. Among them, the alkaline storage battery is expected to have high reliability, and the small battery has been used for various portable devices and the large battery has been used for industrial use for any reason that the size and weight can be reduced.

In this alkaline storage battery, an air electrode, a silver oxide electrode, and the like are partly taken up as a positive electrode.
In most cases it is a nickel electrode. The characteristics have been improved from the pocket type to the sintering type, and the sealing has been made possible and the use has expanded.

On the other hand, in addition to cadmium, zinc, iron, hydrogen and the like are targeted for the negative electrode. At present, cadmium electrodes are mainly used. 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.

[0005] A hydrogen storage alloy electrode of an alkaline storage battery using 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 dendrite formation. Therefore, it is expected as a negative electrode for an alkaline storage battery having a long life, no pollution, and a high energy density.

[0006] The alloy used for such a hydrogen storage alloy electrode is usually produced by an arc melting method or a high-frequency induction heating melting method, and is generally a Ti-Ni-based or La (or Mm) -Ni-based multiple element. Series alloys are well known. T
i-Ni-based multi-component alloys are AB type (A: La, Z
elements having high affinity for hydrogen, such as r and Ti, B: N
i, Mn, Cr, etc.)
As a feature, although a relatively large discharge capacity is exhibited at the beginning of the charge / discharge cycle, 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 system multi-alloy has recently extensively developed advanced as an electrode material, in particular Mm-Ni system multi-component alloys are already in practical use, this alloy system However, there are also problems such as a relatively small discharge capacity, insufficient life performance as a battery electrode, and a high material cost. Therefore, a new hydrogen storage alloy material having a larger discharge capacity and a longer life is desired.

[0007] On the other hand, AB ₂ type Loves
Phase alloys have a relatively high hydrogen storage capacity and are promising as high capacity and long life electrodes. Already for this alloy system
For example, a ZrMoαNiβ-based alloy (JP-A-64-4837)
No. 0) and AxByNiz-based alloys (JP-A-1-102)
855), ZrαMnβMoγCrδNiε (Japanese Patent Application No. 2-174741).

[0008]

However, AB ₂
When a Laves phase alloy of the type is used for the electrode, Ti-
Although the discharge capacity is large and the life can be extended as compared with a Ni-based or La (or Mm) -Ni-based multi-component alloy, it is desired to further improve the performance. Then, by restricting the alloy system to the Zr-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 (Japanese Patent Application No. Hei. 174741
issue). Further, the homogeneity of the alloy was improved by further increasing the amount of Mn and limiting the amount of Cr, and by substituting a part of Mo with V, the hysteresis in the hydrogen absorption-desorption process was reduced, and the discharge capacity was further increased. .

However, when a nickel-hydrogen storage battery is constructed using such a hydrogen storage alloy electrode, the temperature of the storage battery increases due to the heat of hydrogenation of the negative electrode hydrogen storage alloy during rapid charging. For this reason, there has been a problem that the hydrogen equilibrium pressure of the negative electrode hydrogen storage alloy increases, the gas pressure in the battery increases, and the liquid leakage and the hydrogen storage amount decrease significantly.

The present invention solves the above-mentioned conventional problems. By improving the hydrogen storage alloy, the gas pressure in the battery can be kept low even in a high temperature state (for example, about 80 ° C.) during rapid charging. An object of the present invention is to prevent liquid leakage and maintain a high capacity of hydrogen storage.

[0011]

In order to achieve the above object,
Therefore, the hydrogen storage alloy electrode of the present invention has a general formula: ZrMn
_wV_bMo_xCr_yNi_z(However, 0.5 <w ≦ 0.
8, 0 <b <0.3, 0 <x <0.3, 0 <y ≦ 0.
2, 0.8 ≦ z <1.2, and 0.1 ≦ b + x ≦
0.3, 2.0 ≦ w + b + x + y + z ≦ 2.4)
The main component of the alloy phase is C15 (MgCu_Two) Type Love
the s phase, and its crystal lattice constant (a) is 7.05
Angstrom ≦ a ≦ 7.13 angstroms
Using hydrogen storage alloy or its hydride
It is provided with.

In the above structure, Cr, V and Mo
Is y ≦ b + x, and Ni, V and M
It is preferable that the compounding ratio of o is zbx ≦ 1.2.
No. Next, the method for producing a hydrogen storage alloy electrode of the present invention is generally
The formula is ZrMn_wV_bMo _xCr_yNi_z(However,
0.5 <w ≦ 0.8, 0 <b <0.3, 0 <x <0.
3,0 <y ≦ 0.2, 0.8 ≦ z <1.2, and
0.1 ≦ b + x ≦ 0.3, 2.0 ≦ w + b + x + y + z
≦ 2.4), and the main component of the alloy phase is C15 (MgC
u_Two) Type Laves phase and its crystal lattice constant
(A) is 7.05 angstroms ≦ a ≦ 7.13
Hydrogen storage alloy or its hydride
At a temperature in the range of 1000 to 1300 ° C. and in a vacuum.
Or homogenizing heat treatment in an inert gas atmosphere.
It has a configuration.

[0013]

According to the structure of the present invention, the general formula is ZrM
_{n w V b Mo x Cr y} Ni z ( however, 0.5 <w ≦
0.8, 0 <b <0.3, 0 <x <0.3, 0 <y ≦
0.2, 0.8 ≦ z <1.2, and 0.1 ≦ b +
x ≦ 0.3, 2.0 ≦ w + b + x + y + z ≦ 2.4), and the main component of the alloy phase is C15 (MgCu ₂ ) type La
ves phase and its crystal lattice constant (a) is 7.
By using a hydrogen storage alloy or its hydride satisfying 05 angstroms ≦ a ≦ 7.13 angstroms, the gas pressure in the battery is maintained at a low pressure even in a high temperature state (for example, about 80 ° C.) at the time of rapid charging, and liquid leakage is prevented. At the same time, a high capacity hydrogen storage amount can be maintained. That is, the hydrogen-absorbing alloy electrode of the present invention uses the conventional Zr-M
An improved nV-Mo-Cr-Ni-based hydrogen storage alloy, in which the hydrogen equilibrium pressure in a high temperature state (eg, about 80 ° C.) during rapid charging is reduced by reducing the amount of Ni in the conventional alloy composition. It was made. Ni in alloy
Is essential for the alloy to electrochemically store and release hydrogen. When the amount of Ni decreases, the electrochemical activity decreases, but the amount of hydrogen storage increases, so that the discharge capacity of the conventional hydrogen storage alloy electrode can be substantially maintained.

Therefore, an alkaline storage battery, such as a nickel-metal hydride storage battery, formed by using the electrode of the present invention can maintain the gas pressure in the battery at a low pressure even in a high-temperature state at the time of rapid charging as compared with a conventional battery. , And has a high capacity.

Next, according to the structure of the manufacturing method of the present invention, the hydrogen storage alloy electrode can be efficiently and rationally manufactured. The reason for setting the heat treatment temperature in the range of 1000 to 1300 ° C. is that if the temperature is lower than 1000 ° C., the effect of the heat treatment is low, and if it exceeds 1300 ° C., Mn of the alloy is evaporated and the alloy composition is destroyed. The reason why the homogenization treatment is performed in a vacuum or in an inert gas atmosphere is to prevent oxidation of the alloy surface.

[0016]

An embodiment of the present invention will be described below with reference to the drawings. Commercially available Zr, Mn, V, Mo, Cr, Ni
An alloy having a composition as shown in (Table 1) 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 content was 0.8 or more, when produced in an arc furnace, a large amount of Mn was evaporated, and it was difficult to obtain a target alloy.
Next, heat treatment was performed in vacuum at 1100 ° C. for 12 hours to obtain an alloy sample.

[0017]

[Table 1]

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

Sample No. Sample Nos. 1 to 5 are comparative examples having different constituent elements or composition ratios from the present invention. Nos. 6 to 15 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, the main component of the alloy phase was C
It was confirmed to be a 15 type Laves phase (MgCu ₂ type fcc structure). Also, after heat treatment in vacuum, the peak of fcc became larger and sharper than before heat treatment, so that heat treatment increased the proportion of C15-type Laves phase and improved the homogeneity and crystallinity of the alloy. all right. In particular, it was confirmed that a target alloy having a uniform composition was obtained even when the Mn content was 0.8 or more. The crystal lattice constant was 7.05 to 7.13 angstroms in each case.

Next, a PCT measurement was performed at 70 ° C. for each alloy sample. Sample No. In alloy samples other than Sample No. 1, the hysteresis of the hydrogen absorption-desorption process was small,
o. It was found that the ratio was 1/5 to 1/10 as compared with 1. FIG. 1 shows the relationship between the hydrogen storage amount up to a hydrogen gas pressure of 5 kg / cm ² and the hydrogen equilibrium pressure. The amount of hydrogen occlusion was shown in terms of an amount of electricity (mAh / g) for comparison with the discharge capacity of the alloy due to electrochemical charging and discharging reactions. FIG.
The results, reduced the hydrogen equilibrium pressure with the alloy _{ZrMn w V b Mo x Cr y} Ni z of Ni amount z is reduced,
It was found that the hydrogen storage amount increased.

With respect to the alloy samples as described above, 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. Sample N
o. The alloys Nos. 1 to 15 were pulverized so as to have a particle size of 400 mesh or less, and 8 wt.
After immersion at 0 ° C. for 1 hour, it was washed with water and dried. 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 sufficiently mixed and stirred, and pressed to form a disk having a diameter of 24.5 mm and a thickness of 2.5 mm. Molded. This is placed in a vacuum at 130
C. for 1 hour to melt the binder to form a hydrogen storage alloy electrode.

A nickel wire lead is attached to the hydrogen storage alloy electrode to form a negative electrode, a sintered nickel electrode having an excessive capacity as a positive electrode, a polyamide nonwoven fabric as a separator, and a potassium hydroxide aqueous solution having a specific gravity of 1.30. As an electrolyte, charging and discharging were repeated at a constant current at 25 ° C., and the discharge capacity in each cycle was measured. In addition,
The charging condition was 100 mA × 5.5 g of hydrogen storage alloy.
The discharge was performed at 50 mA / g, and the voltage was cut at 0.8 V. The result is shown in FIG.
2 shows the number of charge / discharge cycles on the horizontal axis and the discharge capacity per 1 g of the alloy on the vertical axis. In FIG. Matches. From the results in FIG. In No. 3, since the amount of Mn was very large, it was considered that when immersed in an alkaline solution, the amount of Mn eluted was so large that the alloy composition was greatly shifted, and the discharge capacity was reduced. In addition, the sample No. In Nos. 4 and 5, the discharge capacity was small due to poor electrochemical activity. Discharge capacity alloy samples other than these are the 340 mAh / g or more, particularly _{ZrMn w V b Mo x Cr y} Ni z of Ni amount z is 1.0
It was found that an excellent value was exhibited when the value was ~ 1.1.

Further, using these hydrogen storage alloy electrodes, a sealed nickel-hydrogen storage battery was produced in the following manner. The sample alloys shown in Table 1 were powdered to 400 mesh or less, then treated with an alkali solution in the same manner as described above, washed with water and dried. Each of such alloy powders is mixed with a dilute aqueous solution of carboxymethyl cellulose (CMC) and stirred to form a paste, and as an electrode support, a foamed nickel sheet having an average pore size of 150 microns, a porosity of 95%, and a thickness of 1.0 mm is used. Filled. 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 the electrodes was 3.3 cm wide and 2 cm long.
The thickness was adjusted to 1 cm and the thickness to 0.40 mm, and lead plates were attached to two predetermined positions. And the positive electrode (capacity 3.0 Ah)
In addition, the three layers were spirally formed into a cylindrical shape in combination with a separator and stored in an SC-size battery case. As the positive electrode at this time, a known foamed nickel electrode was selected and used with a width of 3.3 cm and a length of 18 cm. Also in this case, two lead plates were attached. The separator used is a polypropylene nonwoven fabric provided with hydrophilicity, and the specific gravity of the electrolyte is 1.
30 g of lithium hydroxide in 20 potassium hydroxide aqueous solution
/ L dissolved. This was sealed to obtain a sealed battery.

A pressure sensor for measuring the gas pressure in the battery was attached to each of the batteries thus manufactured, and the gas pressure in the battery during rapid charge and discharge was examined. In addition, a thermocouple was attached to the side of the battery to check the change in the battery temperature.

Charge at 30 ° C. 0.1 C (10 hour rate) 12
20% charging / discharging at 0%, discharge 0.2C (5 hour rate), 0.8V cut, activate the hydrogen storage alloy electrode, then charge at 0.2C to a gas pressure of 5kg / cm ^{2 in the} battery. And discharge was performed at a discharge of 0.2 C up to a 0.8 V cut. Next, 5 batteries are put into a plastic container and charged at 3 C (1/3 hour rate), and the gas pressure in the battery is 5 kg / c.
to m ² was charged. At this time, the temperature of each of the batteries increased to about 70 to 80 ° C. during charging. After completion of charging, the battery was cooled to 30 ° C., and then discharged at 0.2 C.
The battery was discharged to 8 V and compared with the discharge capacity at the time of charging 0.2 C.

FIG. 3 shows the discharge capacity at the time of 0.2 C charge and the discharge capacity at the time of 3 C charge of the battery using the hydrogen storage alloy electrode of each sample. From the results of FIG. It is considered that in Examples 1 and 2, since the amount of Ni was large, the hydrogen equilibrium pressure was increased due to the temperature rise of the battery during 3C charging, and the discharge capacity was reduced. In addition, the sample No. In Nos. 3 to 5, the capacity as an alloy electrode was small, so that the discharge capacity at the time of charging at 0.2C and 3C was low. In contrast, it was found that when the hydrogen storage alloy electrode of the present invention was used, the discharge capacity at the time of 0.2 C charge and the discharge capacity at the time of 3 C charge were the highest.

Here, the operation of the alloy composition of the present invention will be described. The range of each composition is intended mainly to secure the amount of hydrogen storage and release, and to keep the hydrogen equilibrium pressure low even when the battery temperature rises during rapid charging. Mn improves the homogeneity of the alloy and increases the hydrogen storage capacity. V and Mo lower the hydrogen equilibrium pressure and contribute to an increase in the amount of hydrogen storage and release. In particular, V has the effect of reducing the hysteresis of the hydrogen storage-release process. Ni raises the hydrogen equilibrium pressure and causes a decrease in the amount of hydrogen storage and release, but contributes to an improvement in the activity for electrochemical storage and release of hydrogen.

Each metal element coordinated at the B site of the AB ₂ type alloy provides the above-described effects to the alloy. ZrMn
For _{w V b Mo x Cr y Ni} z, but the amount of Mn w discharge capacity alloy surface tends to be corroded by the alkaline electrolyte exceeds 0.5 is lowered, the prealloyed surface is immersed in an alkaline solution By eluting Mn and reducing the Mn concentration on the alloy surface, corrosion of the alloy surface in the electrolytic solution can be prevented. Therefore, when the Mn content w is 0.5 <w, the homogeneity of the alloy becomes extremely large, and the amount of hydrogen storage and release increases. However, when the Mn content exceeds 0.8, a large amount of Mn is eluted by the alkali solution treatment, and the alloy composition is largely shifted, so that the discharge capacity is reduced. Therefore, Mn
The amount w is suitably 0.5 <w ≦ 0.8. In the case of Cr
When Cr is contained, the C14-type Laves phase (MgZn _2- type hexagonal structure) is easily mixed, and the Cr amount y is 0.2.
Exceeds the hydrogen absorption rate,
Emissions are reduced.

Since V and Mo have a large atomic radius, V
If the sum of the amount b and the Mo amount x exceeds 0.3, the homogeneity of the alloy becomes poor, and conversely, the amount of hydrogen storage and release decreases. Also,
When the Ni amount z is too large and the balance between the V amount b and the Mo amount x is lost, the hydrogen storage-release amount decreases. Therefore, considering the balance between the V amount b, the Mo amount x, and the Ni amount z, zbx ≦ 1.2 is better.

Further, at the time of quick charging, the battery temperature is 70 to
Since the temperature rises to 80 ° C., even in such a temperature range, an alloy having a low hydrogen equilibrium pressure and an Ni content z of less than 1.2 is advantageous in that the amount of absorbed and released hydrogen is large. However, if z is 0.
With an alloy less than 8, sufficient electrochemical activity cannot be obtained due to a small amount of Ni.

From the above, 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 even during rapid charging.

[0033]

The hydrogen storage alloy electrode of the present invention can store and release a large amount of hydrogen even during rapid charging by suppressing the hydrogen equilibrium pressure at a high temperature of the alloy. The alkaline storage battery has excellent discharge characteristics without impairing high capacity as compared with the conventional battery.

[Brief description of the drawings]

FIG. 1 is a correlation diagram between the hydrogen storage amount at 70 ° C. and the hydrogen equilibrium pressure in Examples of the present invention and a conventional example.

FIG. 2 is a charge / discharge cycle characteristic diagram showing evaluation results of a unit cell of an example of the present invention and a conventional example.

FIG. 3 is a discharge characteristic diagram at the time of rapid charging of the positive-electrode capacity-regulated batteries of the example of the present invention and the conventional example.

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tsutomu Iwaki 1006 Kazuma, Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) References JP-A-6-96762 (JP, A) JP-A-4- 301045 (JP, A) JP-A-3-28941 (JP, A) JP-A-1-102855 (JP, A) JP-A-1-60961 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 4/38 H01M 4/24-4/26

Claims (3)

(57) [Claims] 1. A general _{formula, ZrMn w V b Mo x Cr} y
Ni _z (where 0.5 <w ≦ 0.8, 0 <b <0.
3, 0 <x <0.3, 0 <y ≦ 0.2, 0.8 ≦ z <
1.2 and 0.1 ≦ b + x ≦ 0.3, 2.0 ≦
w + b + x + y + z ≦ 2.4), the main component of the alloy phase is a C15 (MgCu ₂ ) type Laves phase, and its crystal lattice constant (a) is 7.05 Å ≦ a ≦ 7.13 Å. A hydrogen storage alloy electrode using a hydrogen storage alloy or a hydride thereof. 2. The composition ratio of Cr, V and Mo is y ≦ b.
+ X and the compounding ratio of Ni, V and Mo is z-
The hydrogen storage alloy electrode according to claim 1, wherein b−x ≦ 1.2. 3. A general _{formula, ZrMn w V b Mo x Cr} y
Ni _z (where 0.5 <w ≦ 0.8, 0 <b <0.
3, 0 <x <0.3, 0 <y ≦ 0.2, 0.8 ≦ z <
1.2 and 0.1 ≦ b + x ≦ 0.3, 2.0 ≦
w + b + x + y + z ≦ 2.4), the main component of the alloy phase is a C15 (MgCu ₂ ) type Laves phase, and its crystal lattice constant (a) is 7.05 Å ≦ a ≦ 7.13 Å. A method for producing a hydrogen storage alloy electrode in which a hydrogen storage alloy or a hydride thereof is subjected to a homogenizing heat treatment in a temperature range of 1000 to 1300 ° C. in a vacuum or an inert gas atmosphere.