JP2752099B2 - Method for producing nickel electrode for alkaline battery - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a nickel electrode for an alkaline storage battery using nickel hydroxide as an active material.

2. Description of the Related Art There are various methods for producing nickel electrodes for alkaline storage batteries, such as a sintering method, a pocket method, and a paste method. Widely used. In this sintering manufacturing method, a carbonyl nickel powder is applied on a nickel-plated iron patch metal, which is then sintered to form a substrate, and then a nickel salt solution is permeated into the substrate. Then, nickel is converted into nickel hydroxide by heating or a chemical method. However, in the sintering production method, the step of filling the active material becomes more complicated due to the fine pore size.

Therefore, as shown in JP-A-58-161252, a manufacturing method has been proposed in which a porous metal body is used instead of a sintered body. The metal porous body has a porosity of 95 to 98% and a large pore size of several tens to several hundreds of microns. Therefore, since the active material powder such as nickel hydroxide can be filled as it is, there is an advantage that a nickel electrode for an alkaline storage battery can be easily produced as compared with the above-mentioned sintering method. . In addition, there are a dry method and a wet method in the active material filling method of the electrode using the metal porous body,
The wet method is preferable in consideration of productivity.

By the way, the characteristics of the nickel electrode largely depend on the physical properties of the active material to be filled. In this case, when only nickel hydroxide is used as an active material, oxygen is easily generated in high-temperature charging, so that charging efficiency is reduced. As a method for preventing this, it is generally known to add cadmium as a counter electrode active material. For example, JP-A-57-2059
As shown in Japanese Patent Publication No. 68, if a cadmium layer is formed on the surface of nickel hydroxide, the charging efficiency does not decrease even at high temperature charging.

Here, as a method of adding cadmium to the surface of nickel hydroxide, the following method is known.

A method in which cadmium is added to the surface during the production of nickel hydroxide.

A method in which cadmium hydroxide or cadmium oxide is added to an active material containing nickel hydroxide as a main component (Japanese Patent Laid-Open No.
No. 33758).

Problems to be Solved by the Invention However, the method (1) has a problem that the properties (such as bulk density) of nickel hydroxide change and a step of adding cadmium is separately required, which complicates the manufacturing process. I was

In the above method, when cadmium hydroxide is simply added, it is difficult to add cadmium to the surface, and the effect of addition cannot be sufficiently exhibited. On the other hand, when cadmium oxide is added, the effect of adding cadmium hydroxide is larger than when cadmium hydroxide is added. Changes over time. For this reason, there has been a problem that the slurry becomes unstable and is not suitable for mass production in a process.

Accordingly, an object of the present invention is to provide a method for producing a nickel electrode for an alkaline battery, which is suitable for mass production without complicating the production process and can sufficiently exhibit the effect of adding cadmium to the surface.

Means for Solving the Problems In order to achieve the above object, the present invention provides a cadmium oxide and a phosphate, silicate for preventing hydration of the cadmium oxide, in an active material powder containing nickel hydroxide as a main component. A first step of preparing an active material paste by adding and mixing a hydration inhibitor consisting of arsenate or chromate and water, and a second step of holding the active material paste on a porous metal body.
And a third step of drying and pressing the active material paste.

Function As in the above configuration, if a hydration inhibitor for preventing hydration of cadmium oxide is added in the first step of preparing the active material paste, cadmium oxide does not hydrate in the subsequent steps, so that the slurry No change over time. Therefore, the effect of adding cadmium to the surface can be sufficiently exhibited.

Here, examples of the hydration inhibitor include phosphate, silicate, arsenate and chromate. It is not clear that such oxyacid salts prevent hydration of cadmium oxide,
This is presumably because the addition of the oxyacid salt forms a cadmium oxide thin film on the cadmium oxide surface, and this thin film suppresses the reaction between cadmium oxide and water.

In addition, cadmium is added to the surface by forming complex ions of cadmium and phosphate ions in the paste, and depositing the complex ions on the surfaces of the nickel hydroxide particles during drying.

EXAMPLES [Examples] First, nickel hydroxide, cobalt hydroxide,
95: 5: Cadmium oxide and sodium dihydrogen phosphate
Mix at a ratio of 3: 0.02, and further add water to make a paste.

Next, after filling and holding the paste in sponge nickel, the sponge nickel is pressed to produce a nickel electrode plate. Next, an AA cell was manufactured using the nickel electrode plate and the cadmium electrode plate.

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

[Comparative Example I]

An AA cell was produced in the same manner as in the above example, except that nickel hydroxide and cobalt hydroxide were mixed at a ratio of 95: 5, and water was further added to produce a paste.

The cell fabricated in this manner is hereinafter referred to as a (B) cell.

(Comparative Example II)

Nickel hydroxide, cobalt hydroxide, and cadmium hydroxide were mixed at a ratio of 95: 5: 3, and except that water was added thereto to prepare a paste, in the same manner as in the above example.
An AA cell was fabricated.

The cell fabricated in this manner is hereinafter referred to as a (C) cell.

(Comparative Example III)

Nickel hydroxide, cobalt hydroxide, and cadmium oxide were mixed at a ratio of 95: 5: 3, and AA was prepared in the same manner as in the above example, except that water was added thereto to prepare a paste.
A cell was prepared.

The cell fabricated in this manner is hereinafter referred to as a (D) cell.

Here, the substance mixing ratio of each paste at the time of preparing the above-mentioned cells (A) to (D) is shown in Table 1 below.

[Experiment] Cell (A) of the present invention and cell (B) of Comparative Example
(D) After charging the cell at 70 mA for 16 hours, it was discharged at 700 mA, and the capacity of the battery at this time was examined.
The results are shown in Table 2 below. The discharge is at room temperature (20 ° C)
I went in.

As is clear from Table 2, when charged at 20 ° C., the cells (B) to (D) of the comparative example have 705 to 710 mA, whereas the cell (A) of the present invention has 715 mA. There is no big difference.

However, when the battery is charged at 40 ° C., in the cell (B) in which cadmium hydroxide and cadmium oxide are not added,
518mA, 600C, 616 cells in the (C) cell and (D) cell to which only cadmium hydroxide or cadmium oxide was added.
In contrast to mA, it can be seen that the cell (A) of the present invention to which cadmium oxide and sodium dihydrogen phosphate are added has improved to 658 mA.

In the above example, sodium dihydrogen phosphate was added to the active material, but it was confirmed by experiments that the same effect was obtained even when sodium dihydrogen phosphate was dissolved in water in advance. did.

In the above embodiment, sodium dihydrogen phosphate is used as a hydration inhibitor for the cadmium oxide powder. However, the present invention is not limited to this, and other phosphates, silicates, and arsenic acids may be used. The same effect can be obtained with salts and chromates.

Effects of the Invention As described above, according to the present invention, since cadmium oxide does not hydrate, the effect of adding cadmium to the surface can be sufficiently exhibited.

At this time, since only a hydration inhibitor such as phosphate is added at the time of preparing the paste, the production process of the electrode plate does not become complicated, and the slurry does not become unstable. It also has the effect of being excellent.

 ────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Taimeo Hamamatsu 2-18 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (56) References JP-A-62-108458 (JP, A) 1988-178446 (JP, A)

Claims (1)

(57) [Claims] 1. A hydration comprising cadmium oxide and a phosphate, silicate, arsenate or chromate for preventing hydration of the cadmium oxide in an active material powder mainly composed of nickel hydroxide. A first step of preparing an active material paste by adding and mixing an inhibitor and water, a second step of holding the active material paste in a porous metal body, and a third step of drying and pressing the active material paste. A method for producing a nickel electrode for an alkaline storage battery, comprising: