JP2966492B2 - Manufacturing method of hydrogen storage alloy electrode - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a hydrogen storage alloy electrode used for a negative electrode of a metal-hydrogen alkaline storage battery.

2. Description of the Related Art In recent years, a metal-hydrogen alkaline storage battery capable of achieving a higher energy density than a nickel-cadmium battery has attracted attention as a new alkaline storage battery replacing the nickel-cadmium battery.

A hydrogen storage alloy is used as a negative electrode of this battery. As an example of a method for manufacturing the hydrogen storage alloy, a process of melting and cooling an alloy material to produce a hydrogen storage alloy ingot, Pulverizing the ingot in an alkaline solution to produce a hydrogen storage alloy powder.

However, in the above-mentioned conventional method, since the highly alkaline solution belonging to Group Ia (such as KOH) is used during the pulverizing step of the hydrogen storage alloy ingot, the components of the hydrogen storage alloy are eluted. I do. For this reason, the surface energy of the alloy is increased, and the alloy easily reacts, and the alloy surface is easily corroded, so that pulverization or the like occurs. As a result, the high-rate discharge characteristics deteriorate,
There was a problem that the cycle characteristics deteriorated.

The present invention has been made in view of such circumstances, and has as its object to provide a method of manufacturing a hydrogen storage alloy electrode that can improve high-rate discharge characteristics and cycle characteristics.

Means for Solving the Problems In order to achieve the above object, the present invention provides a first step of producing a hydrogen storage alloy ingot by melting and cooling a hydrogen storage alloy material; In the table
The method is characterized by comprising a second step of preparing a hydrogen storage alloy powder by pulverizing in an alkaline solution containing Group IIa metal ions, and a third step of washing the hydrogen storage alloy powder with water.

Operation According to the production method described above, in the step of preparing the hydrogen storage alloy powder, a Group IIa hydroxide is generated without using a highly alkaline solution. Therefore, the elution of the components of the hydrogen storage alloy in the above step can be prevented, and the reactivity of the alloy decreases.
As a result, it is possible to suppress the pulverization or the like due to corrosion of the alloy surface.

Embodiment An embodiment of the present invention will be described below with reference to FIGS.

〔Example〕

FIG. 1 is a cross-sectional view of a cylindrical nickel-hydrogen alkaline storage battery using electrodes manufactured by the manufacturing method of the present invention, and shows a positive electrode 1 made of sintered nickel, a negative electrode 2 containing a hydrogen storage alloy, The electrode group 4 including the separator 3 interposed between the two poles 1 and 2 is spirally wound. The electrode group 4 is disposed in an outer can 6 that also serves as a negative electrode terminal. The outer can 6 and the negative electrode 2 are connected by a negative electrode conductive tab 5. A sealing body 8 is mounted on an upper opening of the outer can 6 via a packing 7, and a coil spring 9 is provided inside the sealing body 8. The coil spring 9 is configured such that when the internal pressure inside the battery rises abnormally, it is pressed in the direction of arrow A and the gas inside is released to the atmosphere. The sealing body 8 and the positive electrode 1 are connected by a positive electrode conductive type 10.

Here, the cylindrical nickel-hydrogen alkaline storage battery having the above structure was produced as follows.

First, commercially available Mm (mixture of misch metal: rare earth element), Ni, Co, Mn and Al are weighed so that the element ratio becomes 1: 3.2: 1: 0.6: 0.2, and then, in a high frequency melting furnace. By melting and making a melt, and further cooling this melt,
An ingot of an alloy represented by MmNi _3.2 CoMn _0.6 Al _0.2 was prepared. Next, the ingot was pulverized in an aqueous solution containing Mg ions to a particle size of 50 μm or less. The pH of the above aqueous solution
Is 12.

Thereafter, PT as a binder is added to the hydrogen storage alloy powder.
5 wt% of FE (polytetrafluoroethylene) powder is added and kneaded to prepare a paste. Further, this paste is pressed against both surfaces of a current collector made of punching metal to form a negative electrode 2.
Was prepared.

Next, the negative electrode 2 and a sintered nickel positive electrode 1 having a sufficiently larger capacity than the negative electrode 2 were wound via a separator 3 made of a non-woven fabric to produce an electrode group 4. Thereafter, the electrode group 4 is inserted into the outer can 6 and further 30% by weight.
Is injected into the outer can 6, and then the outer can 6
Was sealed to produce a cylindrical nickel-hydrogen storage battery. The theoretical capacity of the battery thus manufactured is 1000 mAh.

The battery fabricated in this manner is hereinafter referred to as (A) battery.

(Comparative example)

A battery was produced in the same manner as in the above example, except that the ingot was pulverized in a KOH solution.

The battery fabricated in this manner is hereinafter referred to as (X) battery.

[Experiment I]

The cycle characteristics of the battery (A) using the electrode manufactured by the manufacturing method of the present invention and the battery (X) using the electrode manufactured by the manufacturing method of the comparative example were examined. It was recognized that the life of the battery A) was extended by about 200 to 300 cycles compared to the battery X.

This is because, in the battery (X), when the hydrogen storage alloy ingot is pulverized, the components of the hydrogen storage alloy elute and the surface energy of the alloy increases, so that the alloy surface easily reacts and the surface is corroded. On the other hand, in the case of the battery (A), a Group IIa hydroxide is generated on the surface of the hydrogen storage alloy powder, and the components of the hydrogen storage alloy can be prevented from being eluted. Therefore, it is considered that the reason is that the reactivity of the alloy surface is reduced and the corrosion of the alloy surface can be suppressed.

(Experiment II)

In the pulverization step, the pH of the aqueous solution containing Mg ions was changed, and the relationship between the pH and the cycle life was examined. The results are shown in FIG. The experiment was performed at a charge / discharge current of 2C.

As is apparent from FIG. 2, the cycle life is prolonged when the pH of the solution exceeds 7, and it is recognized that especially when the pH is 10 or more, the cycle life is dramatically increased. Therefore, from the viewpoint of cycle life, the pH of the grinding solution is preferably 10 or more.

(Experiment III)

In the pulverization step, the pH of the aqueous solution containing Mg ions was changed, and the relationship between the pH and the discharge capacity was examined. The results are shown in FIG. The experimental conditions were the same as those in Experiment II, and in this experiment, the measurement was performed using a single pole.

As is clear from FIG. 3, the pH of the solution was 7 or less or
If it exceeds 14, the discharge capacity decreases. Therefore, from the viewpoint of discharge capacity, the pH of the pulverized solution is preferably more than 7 and 14 or less.

According to Experiments II and III, the pH of the pulverized solution is preferably 7 or more, particularly preferably 10 or more and 14 or less.

[Other Matters] In the above examples, metal ions added to the aqueous solution
Although Mg ion was used, the present invention is not limited to this. Any other metal ion of group IIa such as Ca may be used.

II The addition amount of group a ions is based on the total weight of the alloy.
Experiments have confirmed that it is desirable to add 0.01 mol or more.

In the above embodiment, a cylindrical storage battery is used, but the present invention can of course be applied to a flat storage battery.

Effects of the Invention As described above, according to the present invention, elution of the components of the hydrogen storage alloy can be prevented, so that corrosion of the alloy surface can be suppressed. As a result, there is an effect that high-rate discharge characteristics and cycle characteristics can be significantly improved.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a cylindrical nickel-hydrogen alkaline storage battery using the electrode of the present invention, FIG. 2 is a graph showing the relationship between the pH of a crushed aqueous solution and the number of cycles, and FIG.
6 is a graph showing a relationship between the discharge capacity and the discharge capacity. 1 ... Positive electrode, 2 ... Negative electrode, 3 ... Separator.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-141258 (JP, A) JP-A-3-263760 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01M 4/24-4/26 H01M 4/38 B22F 9/04 C22C 19/00

Claims (1)

(57) [Claims] A first step of dissolving and cooling the hydrogen storage alloy material to produce a hydrogen storage alloy ingot; and applying the hydrogen storage alloy ingot to an alkaline solution containing a metal ion of Group IIa in the periodic table. A second step of producing a hydrogen storage alloy powder by pulverizing in a hydrogen storage alloy powder; and a third step of washing the hydrogen storage alloy powder with water.