JPH05135765A - Manufacture of hydrogen storage electrode - Google Patents

Abstract

PURPOSE:To improve the initial activity, utilization factor, and life characteristic by applying high-temperature alkaline treatment to a hydrogen storage alloy electrode. CONSTITUTION:A hydrogen storage alloy expressed by ZrMn0.6Co0.1V0.2Ni1.2 which is one of C15 type Laves-phase alloys is molded into an electrode, then it is dipped in a 31%-KOH solution at 100 deg.C for 2hr, for example. This electrode is used for a negative electrode, a well-known nickel oxide electrode is used for a positive electrode to constitute a battery, the initial activity is sharply improved, and the utilization factor and life characteristic are improved.

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 then be used in alkaline storage batteries such as nickel-hydrogen storage batteries.

[0002]

2. Description of the Related Art Lead storage batteries and alkaline storage 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, most of the positive electrodes are nickel electrodes, although some of them are air electrodes or silver oxide electrodes. 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, in addition to cadmium, zinc, iron, hydrogen, etc. are targeted.

Recently, in order to achieve a higher energy density, a nickel-hydrogen storage battery using a hydrogen storage alloy electrode has attracted attention, and many proposals have been made for its production method.

As a method for producing a hydrogen storage alloy electrode, there are a method of sintering alloy powder and a paste method of filling or coating a porous support such as foamed, fibrous or punched metal. Of these, the simplest method is the paste method.
Since hydrogen storage alloys are relatively excellent in electron conductivity in the same manner as cadmium electrodes and zinc electrodes, the possibility of non-sintered electrodes is great. That is, it is formed into a paste with a binder and is filled or adhered to a porous conductive plate having a three-dimensional or two-dimensional structure.

Among them, 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 particle surface of the hydrogen storage alloy powder with nickel or copper is particularly resistant to oxidation. , Known to improve utilization, moldability. Further, in order to improve the characteristics, a process such as heat treatment in a vacuum after making the alloy or dipping in an alkaline solution has been proposed.

Further, in the case of applying it to a closed type, addition of a fluorine resin or a catalyst has been attempted in order to improve the absorption of oxygen gas generated from the positive electrode during overcharge.

[0008]

The battery using the hydrogen storage alloy is improved in charge / discharge characteristics, utilization rate and high rate discharge characteristics at the initial stage of charge / discharge cycle. In particular, a hydrogen storage alloy electrode mainly composed of a Zr—Ni type AB ₂ type Laves phase has a high capacity, but there is 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 hydrogen storage alloys.

[0010]

To solve this problem, the present invention oxidizes the surface of the hydrogen storage alloy in an alkaline solution. The alkali treatment in this case is carried out under much more severe conditions, whereas the conventional alkali treatment was selected at 40 to 80 ° C. for the purpose of dissolving and removing the soluble metal which is not a perfect alloy in the alloy. That is, 95 ° C or higher,
About 100 to 120 ° C is necessary. The time is 0.5
~ 5 hours is enough.

In particular, the general formula of hydrogen storage alloy is AB
It is represented by 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 C14 type with symmetry and / or C15 type with cubic symmetry.

As the alkali, the specific gravity is 1.20 (2
A potassium hydroxide solution at 0 ° C. or higher is preferable, but a caustic solution such as sodium hydroxide or lithium hydroxide is also effective.

[0013]

Function As a means for improving the capacity of the hydrogen storage alloy, stabilizing the performance and extending the life of the hydrogen storage alloy, alkali treatment may be performed by immersing the hydrogen storage alloy in an alkaline solution. This is to remove in advance the metal that may dissolve after being made into a battery with a metal that does not form the desired alloy due to segregation during alloy production (Japanese Patent Laid-Open No. 63-146353). Therefore, the alkali treatment is performed at a temperature of about 45 to 80 ° C.
It was said that the performance was rather deteriorated at 0 ° C or higher.

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

Also, this effect is
It is very remarkable in the B ₂ type hydrogen storage alloy.

[0016]

[Example] As a hydrogen storage alloy, the main alloy phase is C15
Type Laves phase alloy, ZrMn _0.6 Co _0.1 V
1% by weight of polyethylene powder is added to powder having an average particle size of 25 μm obtained by crushing _0.2 Ni _1.2 alloy with a jet mill, and made into a paste with ethanol. Then, this paste was filled in 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 wt% potassium hydroxide solution at 100 to 105 ° C. for 2 hours. This electrode is designated as A.

Also, an electrode B prepared by immersing the electrode prepared in the same manner in a 30% by weight potassium hydroxide solution at 70 ° C. for 2 hours.

Similarly, 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 designated as electrode C.

These electrodes are used as negative electrodes, and a nickel oxide electrode having an excessive electric capacity is arranged on the counter electrode, and the specific gravity of the electrolyte is 1.
The potassium hydroxide aqueous solution of 30 was used, and the capacity was regulated by the hydrogen storage alloy negative electrode in an open system rich in electrolyte solution, and charging / discharging was performed. Assuming a sealed battery with positive electrode regulation, charging is 0.1 A x 2.5 hours per 1 g of hydrogen storage alloy, discharging is 1 g of alloy
The terminal voltage was up to 0.8 V at 0.05 A.

The results are shown in FIG. In the electrode C, the discharge capacity at the first cycle was 0.1 Ah / g, which was low at the beginning of the charge / discharge cycle, and it took 4 or more cycles until the charge / discharge ratio reached about 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, it took 6 cycles or more for the electrode B to reach a charge / discharge ratio of 1.0 at 0.13 Ah / g in the first cycle. Therefore, the high temperature alkaline treatment at 100 ° C. or higher was very effective for improving the initial activity and utilization rate of the battery, but the conventional alkaline treatment at 70 ° C. which is the conventional alkaline treatment temperature delays the rise of discharge capacity. It was a result.

Further, after that, charging was carried out 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
It was Ah / g, and the alloy utilization rate was also improved.

Next, the results 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 attached lead plates at predetermined two positions. Then, in combination with the positive electrode and the separator, it was made into a cylindrical three-layer spiral shape and housed in an SC size battery case. A known foaming nickel electrode was selected as the positive electrode at this time, and the width was 3.3 c.
m and length 16 cm were used. Also in this case, the lead plates were attached at two places. As the separator, a polypropylene non-woven fabric having hydrophilicity was used. As the electrolyte,
Lithium hydroxide was dissolved in an aqueous potassium hydroxide solution having a specific gravity of 1.25 at 25 g / l and used. This was sealed to form a sealed battery. This battery has a nominal capacity of 3.
It is 0 Ah. The capacity of the negative electrode with respect to the positive electrode was 150%. In this sealed battery, a battery composed of the hydrogen storage alloy electrode A is referred to as a battery A, a battery similarly composed of the electrode B is referred to as a battery B, and a battery using the electrode C is referred to as a battery C.

The results of making 10 of each of these batteries and evaluating them by a charge / discharge cycle test will be described.

First, the initial discharge voltage and capacity were compared. 5
When constant current charge of 150% of capacity at time rate and constant current discharge up to 1.0 V at 5 hour rate were performed at 20 ° C.,
A had an average voltage of 1.28 V and a discharge capacity of approximately 3.0 Ah from the first cycle. Further, it took three cycles for the battery B to reach a discharge capacity of 3.0 Ah at an average voltage of 1.23V. Battery C has an average discharge voltage of 1.2
It was 0 V and required 3 cycles until the discharge capacity reached 3.0 Ah.

Similarly, charging is performed up to 150% per hour,
The discharge was similarly performed at a final voltage of 1.0 V at a rate of 1 hour, and the result of repeating the charge / discharge cycle at 20 ° C. was as follows: Battery A had an average discharge voltage of 1.22 V, Battery B had 1.17 V, and Battery C had 1.
It was also found that it was 14 V, and that it had more excellent discharge characteristics in rapid charging / discharging. The battery internal pressure at the end of charging was 1.7 kg / cm ^{2 for} battery A and 5.3 kg / cm ² for battery B.
While it was cm ^2, it was 10 Kg / cm ² or more in the battery C.

Next, using 10 cells for each battery, the charge 1/2 hour rate is 150%, and the discharge 1/2 hour rate is 1.0V.
Life characteristics were compared by charging and discharging with constant current up to. The result is shown in FIG. The discharge capacity of Battery A was 95% at 300 cycles, 88% at 600 cycles, Battery B was 91% at 300 cycles, 78% at 600 cycles, and Battery C was at negative cycle rate control at 300 cycles and the initial rate was 80%. The capacity decreased to%. Therefore, the hydrogen storage alloy electrode according to the present invention has improved life characteristics.

[0027]

INDUSTRIAL APPLICABILITY 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 rate and the life.

[Brief description of drawings]

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

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁵ Identification number Internal reference number FI Technical indication location H01M 4/38 A 8520-4K (72) Inventor Tsuyoshi Iwaki 1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric Sangyo Co., Ltd.

Claims (3)

[Claims] 1. A main hydrogen storage alloy is a Zr—Ni system, a general formula is represented by ABα (α = 1.5 to 2.5), and an alloy phase substantially belongs to a Laves phase of an intermetallic compound. Hydrogen storage alloy powder having a hexagonal symmetry C14 type and / or a cubic symmetry C15 type hydrogen storage alloy powder as an electrode together with a binder and then immersed in an alkaline solution at 100 to 120 ° C. Alloy electrode manufacturing method. 2. A general formula of a 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 ≦
The method for producing a hydrogen storage alloy electrode according to claim 1, which is represented by 2.4). 3. The alkaline solution has a specific gravity of 1.20 (20
3. A potassium hydroxide solution having a temperature of ℃) or higher.
A method for producing the hydrogen storage alloy electrode as described.