JPH0729569A - Manufacture of hydrogen storage alloy electrode - Google Patents

Abstract

PURPOSE:To improve the initial characteristics of an electrode containing a hydrogen storage alloy, the gas absorption characteristics thereof during electric charging, and cycle life thereof by immersing the electrode into an aqueous solution of alkali for a specified time period after the electrode has been electrically charged. CONSTITUTION:After the step of electrically charging an electrode containing a hydrogen storage alloy, this electrode is immersed in an aqueous solution of alkali such as caustic alkali solution, kept at a temperature of 95 to 120 deg., for a specified time period. As a result, the surface of the electrode which is necessary for electric charging and discharging is reformed and, during the electric charging and discharging after the formation of the battery, it is possible to suppress the elution and precipitation of fusible metal. Accordingly the initial characteristics and the gas absorption characteristics are improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a hydrogen storage alloy electrode used in a sealed nickel-hydrogen storage battery or the like.

[0002]

2. Description of the Related Art Alkaline storage batteries that are widely used as various power sources are expected to have high reliability and can be made compact and lightweight. Shape batteries have been used for industrial purposes.
In this alkaline storage battery, an air electrode, a silver oxide electrode, and the like are partially taken as the positive electrode, but in most cases, the nickel electrode is used. Nickel electrode has improved its characteristics from the pocket type to the sintered type, and has become possible to be hermetically sealed and expanded its applications. On the other hand, as the negative electrode, in addition to cadmium, zinc, iron, hydrogen, etc. are targeted. However, at present, the cadmium electrode is mainly used. However, in order to achieve an even higher energy density, a nickel-hydrogen storage battery using a metal hydride, that is, a hydrogen storage alloy as a negative electrode has been receiving attention, and many proposals have been made for a method for manufacturing a hydrogen storage alloy electrode. For example, in order to improve the oxidization and moldability of the hydrogen storage alloy powder, a technique of plating nickel or copper on the surface of the alloy powder to form a porous metal layer on the surface is well known. Furthermore, a method of heat treatment at a high temperature for homogenizing the alloy after manufacturing the alloy, or for the purpose of prolonging the life by dissolving and removing the soluble metal in the alkaline solution which is not a complete alloy in the alloy powder, There is a method of treating the alloy powder or the electrode incorporating the alloy powder with an alkali. In addition to this, various means such as various additives have been taken to improve the stability of the performance and the life.

As a method for producing a hydrogen storage alloy electrode, a method of sintering alloy powder and a method of filling or coating a paste of alloy powder on a foamed or fibrous porous metal body or punching metal or the like. There is a formula. The hydrogen storage alloy used is mainly a multi-element alloy based on rare earth MmNi ₅ . Regarding this, it is desired to further increase the capacity. In addition, Zr (Ti) -N
The AB2-based alloy based on i has a high capacity in the end, but it has some problems in the discharge characteristics in the initial stage of the charge / discharge cycle. In addition, the discharge characteristics of the hydrogen storage alloy electrode at the beginning of the charge / discharge cycle and the gas absorption at the time of charging, which are required for the sealed battery, are important.

[0004]

As a means for improving the capacity of the hydrogen storage alloy electrode, stability of performance, and improvement of life, there is a case where an alkali treatment is carried out by immersing the hydrogen storage alloy powder in an alkaline solution. Its main purpose is to remove in advance a metal that has not been formed into a desired alloy due to segregation or the like at the time of alloy production and may dissolve in the battery after the electrode is formed. Therefore, it is not preferable to immerse the alkaline solution for this purpose under severe conditions in order to dissolve the molten metal and not destroy the desired alloy region. However, when making it into an electrode and then immersing it in an alkaline solution,
Oxidation is included and may be more severe than removal of impurities.
For example, in the case of an AB ₂ -based alloy based on Zr (Ti) -Ni, this treatment causes the surface to completely change from metallic color to blackish brown. As a result, the effect of improving the discharge characteristics at the beginning of the charge / discharge cycle can be obtained. The reason is that the surface of the alloy is oxidized by the alkali and the wettability with the alkali is remarkably improved. On the other hand, even in the case of the Mm-Ni system, which has relatively excellent initial characteristics, the alkali treatment after the electrode configuration makes the alloy surface blackish brown, improving the utilization rate and adding the effect of removing impurities to improve the gas absorption. To be done.

However, only with the alkali treatment after the electrode construction, there is a possibility that a metal that does not form a desired alloy due to segregation or the like seen in the powder treatment inside the electrode may dissolve in the battery after the electrode construction. The effect of removing the metal in advance can hardly be expected. Further, if a harsh alkali treatment such as when treating the electrode in the powder state from the beginning is performed, all the individual particles are oxidized, so that the performance as the electrode is rather deteriorated. Therefore, an object of the present invention is to improve the alkaline treatment as described above to improve the initial characteristics of the hydrogen storage alloy electrode, the gas absorbability during charging, and the cycle life.

[0006]

The present invention is characterized in that an alkali treatment is carried out after a step of charging or charging an electrode containing a hydrogen storage alloy. This alkali treatment is performed at a temperature of about 90 to 120 ° C. In addition,
The time for the alkali treatment may be about 0.5 to 5 hours. As the alkali, a caustic potash aqueous solution having a specific gravity of 1.30 (20 ° C.) or higher is preferable, but caustic soda, lithium hydroxide or the like caustic aqueous solution is also effective.

When a binder such as polyvinyl alcohol or carboxymethyl cellulose having a low electric resistance is used during the production of the hydrogen storage alloy electrode, the binder is destroyed or eluted during the alkali treatment. If the pressure applied during electrode production is sufficient, there is no risk of the alloy powder falling off even if the electrode is wound. However, a binder may be added again. In addition, in order to improve the gas absorbability during charging, it is extremely effective to coat the surface of the electrode with a water-repellent resin powder after the alkali treatment.

[0008]

The present invention utilizes the fact that the hydrogen storage alloy is pulverized by charging. That is, after forming an electrode, charging is performed to form a particle surface that functions as an electrode, and then treatment with an alkali is performed to modify the surface necessary for actual charging / discharging. It suppresses elution and precipitation of soluble metals. According to the present invention, a hydrogen storage alloy electrode having excellent initial characteristics and gas absorption characteristics can be obtained. In addition, applying the water-repellent resin powder on the surface of the electrode after the alkali treatment is extremely effective in improving gas absorption at the time of charging due to a synergistic effect with the alkali treatment.

[0009]

EXAMPLES Examples of the present invention will be described below. ZrMn _0.5 Cr which is one of AB ₂ type alloys as a hydrogen storage alloy
_0.2 V _0.1 Ni _1.2 was crushed, and a 2% by weight aqueous solution of polyvinyl alcohol was added to the powder which passed through a 360-mesh sieve to make a paste.
%, 1.0 mm thick foamed nickel plate. This electrode was cut into a width of 33 mm and a length of 210 mm, and a lead plate was attached by spot welding. Then, the electrode was pressed with a 100 ton press and further passed through a roller press to a thickness of 0.
Adjust to 49 mm.

Then 25 in a 30% by weight aqueous solution of caustic potash
At 0 ° C., the negative electrode is charged at a current of 1.5 A for 5 hours and discharged at 1 A until it is almost completely discharged. The temperature is raised as it is to 110 to 114 ° C. and kept for 1 hour. As a result, there is a black precipitate, and the electrode surface changes from metallic color to blackish brown. This electrode is designated as A.

For comparison, the same hydrogen storage alloy powder as described above is used, and after being alkali-treated at 80 to 82 ° C., an electrode formed by filling a foam nickel plate in the same manner as above is designated as B. In addition, after the electrode is formed in the same manner as above using the same hydrogen storage alloy powder as described above, 110 to 1
Let C be the hydrogen storage alloy electrode treated with alkali at 14 ° C.

First, in order to investigate the characteristics of the three types of negative electrodes, a sintered nickel electrode having a sufficiently large capacity so as to satisfy the negative electrode law was used as a counter electrode, and a sealed battery was assumed.
The separator sandwiched between both electrodes was impregnated with an electrolytic solution prepared by dissolving 20 g / l of lithium hydroxide in a caustic potash solution having a specific gravity of 1.26. When a constant current charge of 140% of the negative electrode capacity was performed at a rate of 5 hours and a constant current discharge at 0.5 A to 0.9 V was repeated, the discharge capacity density of the electrode A was 305 mAh / g at the first cycle and 305 mAh / g at the second cycle. 359 mAh /
At 367th cycle 367 mAh / g, it became almost constant thereafter. However, the electrode B is 241 mAh / in the first cycle.
g, 3rd cycle 298 mAh / g, 5th cycle 34
4mAh / g, almost constant after 8 cycles, 360mAh
/ G. Also, the electrode C is 297 m in the first cycle.
Ah / g, 3rd cycle 332 mAh / g, 5th cycle 354 mAh / g, almost constant after 6th cycle 365
It was mAh / g. From these results, it can be seen that the electrode A has improved cycle initial characteristics and a high utilization rate.

Then, 25 g / each of the above hydrogen storage alloy electrodes, a known nickel electrode, a hydrophilic polypropylene non-woven separator and a caustic potash aqueous solution having a specific gravity of 1.25 were used.
Using an electrolyte solution in which 1 part of lithium hydroxide is dissolved,
A C-type sealed nickel-hydrogen storage battery was constructed. The nominal capacity is 3.0 Ah, and the capacity of the negative electrode with respect to the positive electrode is 15
It is 0%. It should be noted that any of the hydrogen storage alloy electrodes has a commercially available tetrafluoroethylene-6 on the electrode surface for the purpose of improving gas absorption characteristics.
0.5-0.6 mg of fluorinated propylene copolymer resin powder
/ Cm ² is applied. A battery using this electrode A is
A battery using the comparative electrode B is referred to as b, and a battery using the electrode C is referred to as c.

First, the discharge voltage and capacity at the beginning of the cycle were compared. Charged at a constant current of 150% of capacity at a rate of 8 hours,
When the battery was charged and discharged by constant current discharge up to 0.9 V at 5 A, the average voltage of the battery a was 1.24 V in the first cycle, 1.25 V after 2 cycles, and the discharge capacity was almost constant after 2 cycles. It was 0.95 to 3.00 Ah. However, in the battery b, the average voltage in the first cycle is 1.18V.
Therefore, it takes 8 cycles until the discharge capacity is improved and becomes almost constant, and the average voltage is slightly lower than a even at 15 cycles. Battery c has an average voltage of 1.22 V in the first cycle, which is almost the same as battery a, and it takes 3 cycles until the discharge capacity improves and becomes almost constant, and the capacity is 2.4 to 2.6.
Ah, the average voltage was 25 cycles, which was slightly lower than that of the battery a.

Next, using 10 cells for each battery,
The quick charge characteristics were investigated. The ambient temperature is set to 0 ° C., and 1.
When the battery was charged at 0C, the internal pressure of the battery when it was charged to 140% of its capacity was 1.0 kg / cm ² for battery a and b for battery b.
Was 3.7 kg / cm ² and the battery c was 1.6 kg / cm ² . In addition, the battery internal pressure at the time of charging 140% of the capacity by charging 1.3C is 2.5 kg / cm ^{2 for} the battery a,
Battery b is 5.2 kg / cm ² , battery c is 3.1 kg / c
It was m ² . Next, 10 cells of each battery were used, and the capacity was 130 at a temperature of 0.75C at an ambient temperature of 40 ° C.
%, And the life characteristics were compared under the conditions of constant current charging of 1.0% and constant current discharging to 0.9 V at 1.0 C. As a result, the discharge capacities of the batteries a and c at 300 cycles were 97% of the initial values, whereas the discharge capacity was 91% for the battery b and 90% for the battery a at 500 cycles, but the battery b was 90%. It was 75% and battery c was 82%. As is clear from the above results,
It can be seen that the battery a is excellent in rapid charging characteristics and has a long life.

[0016]

As described above, according to the present invention, a sealed nickel-metal alloy having excellent initial characteristics, rapid charging characteristics and long life is provided.
It is possible to obtain a hydrogen storage alloy electrode that provides a hydrogen storage battery.

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Yoichiro Tsuji 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Naoko Maekawa 1006 Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd.

Claims (2)

[Claims] 1. A method for producing a hydrogen storage alloy electrode, comprising a step of charging an electrode containing a hydrogen storage alloy and a step of immersing the electrode in a 95 to 120 ° C. alkaline aqueous solution after charging. 2. A method for producing a hydrogen storage alloy electrode, comprising: a step of charging / discharging an electrode containing a hydrogen storage alloy; and a step of immersing in an alkaline aqueous solution at 95 to 120 ° C. after charging / discharging.