JPH05190175A - Surface treatment of hydrogen storage alloy for alkaline secondary battery - Google Patents

Abstract

PURPOSE:To obtain the hydrogen storage alloy powder which possesses the superior electric charge/discharge characteristic and cycle life characteristic without reducing the productivity by resolviing the troubles of the initial activation and the reduction of electric conductivity which are caused by the precipitation of the excessive oxides to the surface of the alloy. CONSTITUTION:The hydrogen storage alloy powder and an electrode which possesses the superior alkali resistance, initial activation performance, and cycle life characteristic are obtained through the surface treatment method which is constituted of the first step in which a hydrogen storage alloy is prepared and pulverized, second step in which the pulverized hydrogen storage alloy is treated with the mixed aqueous solution of the hydroxides of alkali metals and oxoacid, and the third step in which the hydrogen storage alloy after the alkali treatment is washed by water.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface treatment method for a hydrogen storage alloy used for a negative electrode of an alkaline secondary battery.

[0002]

2. Description of the Related Art In recent years, as a new alkaline secondary battery replacing a nickel-cadmium secondary battery using cadmium as a negative electrode, a nickel-hydrogen storage battery using a hydrogen storage alloy as a negative electrode has been actively researched and developed.

This nickel-hydrogen storage battery can have a long life and high energy density by selecting the type and composition of the hydrogen storage alloy used for the negative electrode.

However, the above hydrogen storage alloy is susceptible to surface oxidation in the alloy crushing process and the electrode manufacturing process,
A dense oxide film is formed on the surface.

When the hydrogen storage alloy powder having such a dense oxide film is used as an electrode, the initial activation of the alloy is hindered or the electric conductivity of the electrode is lowered, resulting in rapid charge / discharge. There is a problem that the charging / discharging efficiency at that time decreases.

Further, the hydrogen storage alloy is easily oxidized in an alkaline electrolyte, and further, the oxidation is promoted by the oxygen gas generated from the positive electrode during overcharge, and hydroxide is generated on the surface, so that the hydrogen storage electrode as the negative electrode is charged. There is a problem that efficiency decreases, a large amount of hydrogen gas is generated in the sealed battery, the internal pressure of the battery rises, liquid leakage and the internal resistance of the battery increase, and the charge / discharge cycle life is shortened.

Therefore, as a method for suppressing the oxidation in the alloy crushing step and the electrode manufacturing step, (a) a method of carrying out both of the above steps in an inert atmosphere, and improvement of oxidation resistance and alkali resistance in the battery As a method of
(B) A method has been proposed in which the hydrogen-absorbing alloy after pulverization is treated with an alkaline aqueous solution to remove the easily-dissolved metal on the alloy surface in advance (JP-A-61-285658).

[0008]

However, in the above method (a), the process is complicated and the productivity is lowered, so that the manufacturing cost of the battery is increased. Further, in the above method (b), a surface layer rich in alkali-resistant metal in the alloy is formed by immersion treatment in an alkaline aqueous solution, while a hydroxide having a composition that dissolves in an alkaline aqueous solution but has a low hydroxide solubility However, there is a problem in that the initial activation of the alloy and the electrical conductivity of the electrode cannot be sufficiently improved because they remain on the surface of the alloy more than necessary.

The present invention has been made in view of the above circumstances, and it is possible to sufficiently improve the initial activation of the alloy and the electric conductivity of the electrode without lowering the productivity, and at the same time, to provide alkali resistance. An object of the present invention is to provide a surface treatment method for a hydrogen storage alloy for secondary batteries.

[0010]

[Means for Solving the Problems] In order to achieve the above-mentioned object, the present invention prepares a hydrogen storage alloy and then pulverizes the hydrogen storage alloy. It is characterized by having a second step of treating with a mixed aqueous solution of a substance and an oxo acid, and a third step of washing the hydrogen storage alloy after the above treatment with water.

The present invention is also characterized in that the alkali metal hydroxide contains at least one of potassium hydroxide, sodium hydroxide and lithium hydroxide.

Further, the above-mentioned oxo acid is characterized by containing at least one of hydroquinone, phloroglucin and vitric acid, except for those having a structure in which hydroxyl groups are bonded to carbons separated from each other.

On the other hand, the concentration of the aqueous solution of the alkali metal hydroxide is characterized by having a specific gravity of 1.10 to 1.50.

Further, the addition concentration of the oxo acid is 0.
It is characterized by being in the range of 005 to 50%.

[0015]

[Function] When treated with an alkaline aqueous solution which is applied as a general method for hydrogen storage alloys, a component having a high solubility in an alkaline aqueous solution is dissolved in the components of the hydrogen storage alloy powder, and a component having a low solubility is a metal. It remains in the state and forms a surface state having excellent alkali resistance.

However, in the case of a hydrogen storage alloy containing a component having a low solubility as a hydroxide, most of it is deposited as a hydroxide on the surface of the alloy powder, which may lead to conductivity and initial activation of the hydrogen storage alloy powder. It cannot be applied because it has an adverse effect.

When treated with a mixed aqueous solution of an alkali metal hydroxide and an oxo acid of the present invention, a stable component of a hydroxide is also dissolved and removed by forming an oxo acid and a chelate compound, so that alkali resistance is not impaired. A surface coating excellent in conductivity and initial activation can be obtained.

[0018]

【Example】

(Example 1) First, commercially available Zr, Mn, V, Co and Ni were used, and Zr: Mn: V: Co: Ni was 1.0: 0.6: 0.2: 0.1: in terms of element ratio. Weighed and mixed to 1.2. The mixture was melted in a vacuum high-frequency furnace to produce an alloy represented by _{ZrMn 0.6 V 0.2 Co 0. 1 Ni} 1.2.

Then, this alloy was mechanically processed to 100 μm.
It was crushed to (average 20 μm) or less. A KOH aqueous solution 11 having a specific gravity of 1.30 is added to 1 kg of the alloy powder (liquid temperature: 80 ° C.) and treated for 60 minutes while stirring (stirring speed: 300 rpm).

Then, carboxymethyl cellulose (hereinafter referred to as CM) as a thickener is added to the alloy powder treated as described above.
C), styrene-butadiene rubber as a binder (hereinafter,
After adding the emulsion of SBR) and water, these were kneaded to prepare a paste. Next, this paste is applied to both sides of a punching metal current collector to prepare a hydrogen storage alloy negative electrode (hereinafter referred to as a hydrogen electrode), and the hydrogen electrode and a known sintered nickel positive electrode (capacity: 1000 mAh). Was wound up through a separator made of non-woven fabric to prepare an electrode body. Next, after inserting this electrode body into a battery can, an electrolytic solution (30 wt% KOH aqueous solution) is injected into the battery can.
Finally, a sealing plate with a safety valve was used for sealing to produce a sealed nickel-hydrogen storage battery.

The battery thus produced is described below in (A)
It is called a battery. (Example 2) An aqueous KOH solution having a specific gravity of 1.30 is added to 1 kg of the alloy powder produced under the same conditions as in Example 1. Further, 50 g of malic acid was added thereto, and the mixture was treated at a liquid temperature of 80 ° C. for 60 minutes while stirring (stirring speed: 300 rpm).

After that, the supernatant liquid is removed, followed by thorough washing with warm water and drying. After that, a battery was produced in the same manner as in (Example 2).

The battery thus manufactured is hereinafter referred to as (B) battery. (Experiment) The battery (A) of (Example 1) and the battery (B) of (Example 2) were each charged and discharged at a current of 1.0 A. The charging time was 150% of the discharging time, and the final discharge voltage was 1.0V.

FIG. 1 shows the fluctuation of the discharge capacity of the battery in this charge / discharge cycle test, and FIG. 2 shows an example of the measurement result of the discharge voltage.

The relationship between the discharge current and the capacity ratio was examined using the battery after one cycle of charge / discharge. Charge condition is 1
A-150% and the final discharge voltage were 1.0V.

The results are shown in FIG. From the results of FIGS. 1, 2 and 3, the discharge capacity of the battery (B) is larger than that of the battery (A) from the beginning, and the capacity and the cycle life are excellent.
In addition, the discharge voltage is high and the high rate discharge characteristics are excellent.

This is treated with a mixed aqueous solution of an alkali metal hydroxide and an oxo acid to give Z on the surface of the alloy powder.
It shows that the conductivity and initial activation properties of the alloy were improved by suppressing the precipitation of hydroxides such as r and Mn.

These results showed similar effects with oxo acids such as lactic acid and glucose.

[0029]

As described above, in the method of the present invention, the hydrogen storage alloy powder is treated with the mixed aqueous solution of the alkali metal hydroxide and the oxo acid, so that the alkali resistance of the hydrogen storage alloy powder is impaired. And the amount of hydroxide formed on the surface is suppressed.

Therefore, if the electrode is made of such powder, the initial activation can be sufficiently achieved, and
Since the contact resistance between particles is reduced and the electrical conductivity of the electrode is improved, the rapid charge / discharge efficiency can be improved.

[Brief description of drawings]

FIG. 1 is the number of cycles at an ambient temperature of 40 ° C. and a charge / discharge rate of 1C-1C in a battery (B) using a hydrogen storage alloy powder subjected to the treatment of the present invention and a battery (A) subjected to an alkali treatment. It is a graph which shows the relationship between a battery capacity.

FIG. 2 is a discharge voltage at an ambient temperature of 20 ° C. and a charge / discharge rate of 1C-1C in a battery (B) using the hydrogen storage alloy powder treated according to the present invention and a battery (A) treated with an alkali. 2 is a graph showing an example of FIG.

FIG. 3 shows an example of a discharge capacity ratio at an ambient temperature of 20 ° C. in a battery (B) using a hydrogen storage alloy powder treated according to the present invention and a battery (A) treated with an alkali. It is a graph.

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

Claims (5)

[Claims] 1. A first step of producing a hydrogen storage alloy, pulverizing the hydrogen storage alloy, and a second step of treating the pulverized hydrogen storage alloy with a mixed aqueous solution of alkali metal hydroxide and oxo acid. And a third step of washing the hydrogen storage alloy afterwards with water, the surface treatment method of the hydrogen storage alloy for alkaline secondary batteries. 2. The surface of the hydrogen storage alloy for an alkaline secondary battery according to claim 1, wherein the alkali metal hydroxide contains at least one of potassium hydroxide, sodium hydroxide and lithium hydroxide. Processing method. 3. The oxo acid comprises at least one of hydroquinone, phloroglucin and viric acid, except for those having a structure in which hydroxyl groups are bonded to carbons separated from each other. A method for treating a surface of a hydrogen storage alloy for an alkaline secondary battery as described above. 4. The alkaline secondary battery according to claim 1, wherein the concentration of the aqueous solution of the alkali metal hydroxide is in the range of specific gravity of 1.10 to 1.50. Surface treatment method for hydrogen storage alloy. 5. The addition concentration of oxo acid is 0.005 to 50.
The surface treatment method for a hydrogen storage alloy for alkaline secondary batteries according to any one of claims 1 to 4, wherein the surface treatment method is in the range of%.