JP3092262B2 - Manufacturing method of hydrogen storage alloy electrode - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode using a hydrogen storage alloy. This electrode can be used for an alkaline storage battery such as a nickel-hydrogen storage battery.

[0002]

2. Description of the Related Art Lead storage batteries and alkaline storage batteries are widely used as various power supplies. Among them, the alkaline storage battery can be 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, the positive electrode is partially an air electrode, a silver oxide electrode or the like, but in most cases 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 as the negative electrode.

In recent years, nickel-hydrogen storage batteries using hydrogen storage alloy electrodes have attracted attention in order to achieve even higher energy densities, and many proposals have been made for manufacturing methods and the like.

[0005] As a method for producing a hydrogen storage alloy electrode, there are a method of sintering an alloy powder and a paste method of filling or coating a porous support such as foamed, fibrous, or punched metal. Of these, the paste method is the simplest one.
Hydrogen storage alloys are relatively excellent in terms of electron conductivity, like cadmium electrodes and zinc electrodes, so that the possibility of non-sintered electrodes is great. That is, the paste is formed into a paste shape together with a binder, and the paste is filled or coated on a porous conductive plate having a three-dimensional or two-dimensional structure.

In order to improve the characteristics of the hydrogen storage alloy electrode, for example, a technique of forming a porous metal layer by plating the surface of the particles of the hydrogen storage alloy powder with nickel or copper has been proposed. It is known to improve the utilization rate and moldability. Further, in order to improve the characteristics, a process has been proposed in which an alloy is heat-treated in a vacuum after being manufactured or immersed in an alkaline solution.

[0007] Further, in the case of application to a closed type, addition of a fluorine resin or a catalyst has been attempted in order to improve the absorbability of oxygen gas generated from the positive electrode particularly during overcharge.

[0008]

A battery using this hydrogen storage alloy is improved in charge / discharge characteristics, utilization factor and high-rate discharge characteristics at the beginning of a charge / discharge cycle. In particular, a hydrogen storage alloy electrode mainly composed of a Zr—Ni-based AB ₂ type Laves phase has a high capacity, but has a problem that the discharge capacity at the beginning of a charge / discharge cycle is small.

An object of the present invention is to improve the initial characteristics and utilization of a hydrogen storage alloy.

[0010]

In order to solve this problem, the present invention oxidizes the surface of a hydrogen storage alloy in an alkaline solution. In this case, the alkali treatment is carried out under much more severe conditions, while the temperature of 40 to 80 ° C. is selected for the purpose of dissolving and removing the soluble metal which is not completely alloyed by the conventional alkali treatment. That is, 95 ° C or more,
About 100 to 120 ° C is required. The time is 0.5
It may be about 5 hours.

The general formula of the hydrogen storage alloy is AB
α (α = 1.5 to 2.5), the alloy phase substantially belongs to the Laves phase of the intermetallic compound, and its crystal structure is 6
This technique is applied to hydrogen storage alloys that are axisymmetric C14 type and / or cubic symmetry C15 type.

The alkali has a specific gravity of 1.20 (2
A potassium hydroxide solution of 0 ° C. or higher is preferred, but a caustic solution such as sodium hydroxide or lithium hydroxide is also effective.

[0013]

As a means for improving the capacity, stabilizing the performance and extending the life of the hydrogen storage alloy, an alkali treatment in which the hydrogen storage alloy is immersed in an alkaline solution may be performed. This is in order to remove in advance the metal which is not formed into a desired alloy due to segregation or the like and which may be dissolved after the battery is manufactured (Japanese Patent Laid-Open No. 63-146353). Therefore, the alkali treatment is performed at a temperature of about 45 to 80 ° C.
At 0 ° C. or higher, the performance was rather inferior.

However, the alkali treatment of the present invention is a more severe surface oxidation treatment than the removal of impurities. Therefore, the surface of the alloy changes from a metallic color to a dark brown color. This is effective in improving the discharge characteristics at the beginning of the charge / discharge cycle, which could hardly be expected by the conventional alkali treatment. The reason is that the surface of the alloy is oxidized by the alkali treatment, and the wettability to the alkali solution is remarkably improved.

[0015] This effect is based on Zr-Ni based A
It is very pronounced in B ₂ type hydrogen storage alloy.

[0016]

EXAMPLE As a hydrogen storage alloy, the main alloy phase was C15.
ZrMn _0.6 Co _0.1 V which is one of the type Laves phase alloys
_To a powder having an average particle size of 25 μm obtained by pulverizing a _0.2 Ni _1.2 alloy by a jet mill, 1% by weight of a polyethylene powder is added, and a paste is formed with ethanol. Then, the paste was filled into a foamed nickel plate having a porosity of 95% and a thickness of 0.8 mm and pressed to obtain an electrode. This was immersed in a 30% by weight potassium hydroxide solution at 100 to 105 ° C. for 2 hours. This electrode is designated as A.

Further, the electrode prepared in the same manner was immersed in a 30% by weight potassium hydroxide solution at 70 ° C. for 2 hours to obtain an electrode B.

In order to compare the characteristics of this electrode, Z
A hydrogen storage alloy having a composition of rMn _0.6 Co _0.1 V _0.2 Ni _1.2 was pulverized, and the obtained alloy powder was used as an electrode without alkali treatment. This is electrode C.

These electrodes are used as a negative electrode, and a nickel oxide electrode having an excessive electric capacity is arranged at a counter electrode, and the specific gravity of the electrolyte is 1.
Using an aqueous potassium hydroxide solution of No. 30, the capacity was regulated with a hydrogen-absorbing alloy negative electrode in an open system rich in electrolyte solution, and charge / discharge was performed. Assuming the case of a sealed battery with positive electrode regulation, charging is 0.1 A x 2.5 hours per gram of hydrogen storage alloy, and discharging is 1 g of alloy.
The terminal voltage was set to 0.8 V at 0.05 A per unit.

FIG. 1 shows the results. Electrode C had a low discharge capacity at the beginning of the charge / discharge cycle of 0.1 Ah / g in the first cycle, and required four or more cycles before the charge / discharge ratio reached approximately 1.0. However, in the case of electrode A, 0.18 Ah / g in the first cycle and 0.25 Ah / g in the second cycle
And the charge / discharge ratio reached 1.0. However, in the electrode B, six cycles or more were required until the charge / discharge ratio reached 1.0 at 0.13 Ah / g in the first cycle. Therefore, high-temperature alkali treatment at 100 ° C. or higher was very effective in improving the initial activity and utilization factor of the battery, whereas alkali treatment at 70 ° C., which is the conventional alkali treatment temperature, conversely delays the rise of discharge capacity. The result was.

Thereafter, charging was performed at 0.55 Ah / g, and the saturation capacity of the alloy was examined.
h / g, electrode B 0.34 Ah / g, electrode C 0.33
Ah / g, and the alloy utilization was also improved.

Next, the result of constructing a sealed battery using this electrode will be described. The electrodes A, B, and C were adjusted to have a width of 3.3 cm, a length of 21 cm, and a thickness of 0.52 mm, and lead plates were attached at two predetermined positions. Then, the resultant was combined with the positive electrode and the separator, spirally formed into three layers in a cylindrical shape, and stored in an SC-size battery case. As the positive electrode at this time, a known foamed nickel electrode was selected, and the width was 3.3 c.
m and a length of 16 cm. Also in this case, two lead plates were attached. In addition, a polypropylene nonwoven fabric provided with hydrophilicity was used as the separator. As the electrolyte,
Lithium hydroxide was dissolved at 25 g / l in an aqueous solution of potassium hydroxide having a specific gravity of 1.25 and used. This was sealed to obtain a sealed battery. This battery has a nominal capacity of 3.
0 Ah. The capacity of the negative electrode with respect to the positive electrode was set to 150%. In this sealed battery, a battery constituted by the electrode A of the hydrogen storage alloy electrode is referred to as a battery A, a battery constituted similarly by the electrode B is referred to as a battery B, and a battery using the electrode C is referred to as a battery C.

A description will be given of the results of preparing 10 batteries each and evaluating them by a charge / discharge cycle test.

First, the initial discharge voltage and the capacity were compared. 5
When a constant current charge of 150% of the capacity at a time rate and a constant current discharge of up to 1.0 V at a rate of 5 hours were performed at 20 ° C.,
A had an average voltage of 1.28 V and a discharge capacity of about 3.0 Ah from the first cycle. Battery B required three cycles to reach a discharge capacity of 3.0 Ah at an average voltage of 1.23 V. In battery C, the average discharge voltage was 1.2
0 V and the discharge capacity required three cycles to reach 3.0 Ah.

Similarly, charging is performed up to 150% at an hourly rate.
The discharge was repeated at a 1-hour rate with a final voltage of 1.0 V and a charge / discharge cycle at 20 ° C. As a result, the average discharge voltage of battery A was 1.22 V, that of battery B was 1.17 V, and that of battery C was 1.
14 V, and it was also found that the battery had more excellent discharge characteristics in rapid charge and discharge. The internal pressure of the battery at the end of charging was 1.7 kg / cm ^{2 for} battery A, and 5.3 kg / cm ² for battery B.
cm ² , whereas the value for battery C was 10 kg / cm ² or more.

Next, 10 cells were used for each battery, and the charging 1/2 hour rate was 150% and the discharging 1/2 hour rate was 1.0 V.
Life characteristics were compared at constant current charging and discharging up to. The result is shown in FIG. The discharge capacity of battery A was 95% in the initial stage after 300 cycles, 88% in the 600 cycles, battery B was 91% in the initial stage in 300 cycles, and 78% in the 600 cycles. %. Therefore, the hydrogen storage alloy electrode according to the present invention also has improved life characteristics.

[0027]

As described above, the hydrogen storage alloy electrode of the present invention can improve the initial activity, which has been a problem in the past, and can improve the utilization factor and the life.

[Brief description of the drawings]

FIG. 1 is a discharge characteristic diagram of an open battery using a hydrogen storage alloy electrode according to one embodiment of the present invention and a conventional example.

FIG. 2 is a discharge characteristic diagram of a sealed battery using a hydrogen storage alloy electrode according to one embodiment of the present invention and a conventional example.

Continued on the front page (51) Int.Cl. ⁷ Identification code FI H01M 4/38 H01M 4/38 A (72) Inventor Tsuyoshi Iwaki 1006 Ojidoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) Reference Document JP-A-2-65060 (JP, A) JP-A-2-17936 (JP, A) JP-A-63-146353 (JP, A) JP-A-64-60961 (JP, A) JP-A-4- 277467 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 4/24-4/26 H01M 4/38 B22F 3 / 26,5 / 00 C22C 16 / 00,30 / 00

Claims (3)

(57) [Claims] A main hydrogen storage alloy is a Zr-Ni-based alloy and the general formula is represented by ABα (α = 1.5 to 2.5), and the alloy phase substantially belongs to the Laves phase of an intermetallic compound. Hydrogen storage characterized in that a hydrogen storage alloy powder having a hexagonal symmetry C14 type and / or a cubic symmetry C15 type is used as an electrode together with a binder, and then immersed in an alkali solution at 100 to 120 ° C. Manufacturing method of alloy electrode. 2. The general formula of the main hydrogen storage alloy is ZrM.
_{n w V x M y Ni z} ( where M is at least one or a mixture selected Cr, Fe, from Co, 0.4 ≦ w
≦ 0.7, 0.1 ≦ x ≦ 0.3, 0 ≦ y ≦ 0.2, 1..
0 ≦ z ≦ 1.5, and 1.8 ≦ w + x + y + z ≦
2. The method for producing a hydrogen storage alloy electrode according to claim 1, wherein the electrode is represented by 2.4). 3. An alkaline solution having a specific gravity of 1.20 (20
C) or more potassium hydroxide solution.
The method for producing a hydrogen storage alloy electrode according to the above.