JPS5816467A - Manufacture of cadmium negative pole - Google Patents

Abstract

PURPOSE:To manufacture of Cd negative pole having high strength and to improve the cell characteristic, by adding the short synthetic resin fiber applied with Cd galvanization into the paste then applying said paste onto the porous core metal thereafter applying the Cd galvanization. CONSTITUTION:The synthetic resin resin short fiber applied with Cd galvanization is dispersed into the paste composed of CdO added with the binder. Then said paste is applied onto the porous core metal and dried to produce the yet- formed plate. Then said plate is applied with Cd galvanization and water washed and dried. The conductive network of metallic Cd is formed in Cd negative pole thus obtained, resulting in the improvement of the oxygen gas absorbing characteristic of the negative pole active substance, the improvement of the utilization of the negative pole active substance and the improvement of the cycle life.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a cadmium negative electrode for alkaline storage batteries, and in particular to a method for producing a cadmium negative electrode for alkaline storage batteries, and in particular, after adding cadmium-plated synthetic resin fibers to a paste and applying the paste to a porous core metal. By applying cadmium plating treatment,
The purpose is to improve battery characteristics such as improving the oxygen gas absorption characteristics of the negative electrode active material, improving the utilization rate of the negative electrode active material, and increasing cycle life, as well as improving the strength of the paste-type negative electrode.

There are three main methods for producing cadmium negative electrodes:

The first is the sintering method, in which nickel powder is sintered in a high-temperature reducing atmosphere to create a porous substrate, and the pores of this substrate are filled with an active material, which has excellent high-rate discharge characteristics. However, it has the disadvantage that it is expensive because it requires the production of a nickel sintered body and the active material filling process is complicated.

The second type is the press type, which has the advantage of being inexpensive to manufacture because it press-molds active material powder together with conductive powder to form an electrode, but has the disadvantage of poor high rate discharge performance and poor cycle characteristics. be.

The third type is called a paste type, in which powder mainly composed of active materials is mixed with a binder to form a paste.
This paste is applied to a porous metal core, and its high rate discharge characteristics are almost similar to those of the sintered type, and the manufacturing process is simpler and cheaper than the sintered type.
In terms of active material utilization rate, oxygen gas absorption characteristics, etc., the sintered type was inferior to the sintered type. In alkaline storage batteries using cadmium negative electrodes, such as sealed nickel-cadmium batteries, the battery Prevents gas accumulation inside. In other words, the nickel positive electrode capacity is made smaller than the negative electrode capacity,
During charging, the nickel positive electrode completes charging first, and oxygen gas is generated from the positive electrode in the overcharge region.

This generated oxygen gas reacts with the metal cadmium of the negative electrode, is evaporated on the cadmium negative electrode, and cadmium hydroxide is generated at the negative electrode, which enables a charging reaction.

Conventional cadmium negative electrodes are used to smoothly eliminate oxygen gas during overcharging and to improve discharge characteristics.
A metal cadmium part was provided in advance during chemical formation.

From the above point of view, conventional paste-type cadmium negative electrodes are made by mixing powder mainly composed of cadmium oxide with a binder to form a paste, applying the paste to a porous core metal, drying it, and applying caustic potassium. It was charged in an alkaline aqueous solution such as an aqueous solution, and metal cadmium was partially formed.

However, this method has the disadvantage that the metal cadmium formed in the negative electrode is unevenly distributed near the core metal and has a low degree of contribution to the discharge reaction and oxygen gas absorption reaction when constructed into a battery.

It is desirable for the metal cadmium to be densely distributed on the electrode plate surface and to form a uniform network within the electrode plate in terms of discharge characteristics, oxygen gas absorption, and active material utilization.

Therefore, in order to increase the electrical conductivity within the negative electrode and improve the utilization rate of the negative electrode active material, a method has been devised in which metal fibers, such as nickel fibers and iron fibers, are added and dispersed during the preparation of the negative electrode paste. However, even when the electrode is pressed, metal fibers are difficult to plastically deform, and they protrude into needles on the electrode and easily short-circuit with the opposing positive electrode through the porous separator during battery construction. There is a drawback.

In addition, a method has been devised in which the surface of the paste negative electrode is plated with cadmium to improve the utilization rate of the active material, but although this method does improve the utilization rate of the active material, it does not improve the life characteristics and discharge characteristics. No improvement has been seen.

In the present invention, by using short synthetic resin fibers plated with cadmium for reinforcing the electrode plate, and by applying cadmium plating to the surface of the electrode plate, the conductivity inside the electrode plate is improved and the electrode plate is plated with cadmium. By making the cadmium distribution in the plate into an ideal shape (cadmium is distributed almost uniformly within the plate and densely distributed on the plate surface), we created a conductive network of metallic cadmium within the negative electrode. Yosi,
The present invention will be described in detail with reference to Examples below, which aim to improve the utilization rate of active materials, improve oxygen gas absorption ability, and improve discharge characteristics (life characteristics).

A mixed powder was prepared by adding 10 parts by weight of carbonyl nickel powder as a conductive material to 100 parts by weight of cadmium oxide, and then short fibers made of polyvinyl chloride resin having a fiber length of 311B and whose surface was plated with cadmium were added and further mixed. 30CG with 1 part by weight of polyvinyl alcohol dissolved in this
Add ethylene glycol solution and knead the whole thing to make a paste.Apply this paste to both sides of a core made of nickel-plated punching metal with a thickness of 0.86, and then dry it to scatter the ethylene glycol. Afterwards, it is pressed to obtain an unformed electrode plate with a porosity of 40%.

Next, for cadmium plating, in which the unformed plate is plated with cadmium, a cadmium cyanide bath, a cadmium fluoride bath, a cadmium sulfate bath, or the like is generally used. In the present invention, cadmium sulfate 100 f/l, sodium sulfate 1
Using a mixed aqueous solution consisting of 00 f/l and 309 f/l of sulfuric acid, cadmium plating was performed on the unformed plate using a metal cadmium plate as a counter electrode.

Note that the current was applied at a current density of 10 mA/csll, and at a current density of 30 mA/csll.
This was a negative electrolytic treatment for 1 minute.

Next, after washing and drying the cadmium electrode plate, o.
It was pressed to a thickness of AOSI and cut into predetermined dimensions to obtain a cadmium unit electrode plate for battery construction.

Using the above-described unit electrode plate according to the present invention, a sintered positive electrode,
A sealed nickel-cadmium storage battery having a nominal capacity of 500 mAh was fabricated by combining it with a separator made of a nonwoven fabric made of polyamide resin.

We investigated the high rate discharge characteristics, cycle life characteristics, and gas absorption capacity characteristics of this battery (A) and the conventional battery (Bl).The only difference between the batteries (A) and (B) is the manufacturing method of the negative electrode. All other conditions were the same.

FIG. 1 shows high rate discharge characteristics, and shows the discharge capacity when a fully charged battery is discharged at various discharge rates.

As is clear from the figure, when the discharge exceeds 30 (1.5 A), it can be seen that the characteristics of the product of the present invention (8) are excellent.

Figure 2 shows the cycle life characteristics, charging at 'A c (26o mA) for 3 hours and discharging at 1 c at 20°C.
(500mA).

While conventional product (B) shows capacity deterioration from around 10 oO cycles, inventive product (3) shows no capacity deterioration, indicating that inventive product (8) is superior in terms of cycle life. .

As mentioned earlier, in sealed nickel-cadmium storage batteries, the oxygen gas generated from the positive electrode during overcharging is absorbed and dissipated on the negative electrode, making it possible to seal the battery, but the size of the oxygen absorption capacity of this negative electrode is , which is important when charging a battery for a short time with a large current.

In other words, if you try to charge with a large current for a short time when the negative electrode has low oxygen absorption capacity, the amount of oxygen generated from the positive electrode will exceed the amount of oxygen absorbed by the negative electrode during overcharging, causing the battery internal pressure to become extremely high. gas leaks out of the battery,
The electrolyte may leak out, causing deterioration of battery characteristics and adverse effects on equipment using batteries.

FIG. 3 shows the oxygen gas absorption capacity of the negative electrode, and shows the internal pressure characteristics when the battery is overcharged, sb, and the internal pressure values when charged at various charging rates at 0°C.

The convex circle of the present invention has a lower battery internal pressure than the conventional product ('@),
It can be seen that the gas absorption ability of the negative electrode is improved.

These improvements in battery characteristics are believed to be due to the following points.

In other words, as mentioned above, while the metal cadmium in the conventional cadmium negative electrode is contained individually in the core plate, the metal cadmium according to the present invention is distributed within the electrode plate by cadmium plating of short fibers. Cadmium is uniformly distributed and densely distributed on the electrode surface where oxygen gas absorption reactions are likely to occur due to cadmium plating on an unformed plate.
It seems that the absorption and disappearance characteristics of oxygen gas are excellent.

In addition, it is thought that the metal cadmium plated on the short resin fibers forms a conductive network within the electrode plate, contributing to the improvement of the discharge characteristics and leading to the improvement of the life characteristics. It is thought that a conductive network leads to an improvement in the utilization rate of the active material of the negative electrode. Therefore, when we investigated the utilization rate of the negative electrode, we found the following.

Utilization rate at each discharge rate using cadmium negative electrodes (A') and (B') similar to those used in the above battery (4, (B)) in a caustic potassium aqueous solution with a concentration of 30% and using a nickel plate as the other electrode. The results were as shown in the table below.

It is thought that the improvement in the utilization rate of the negative electrode active material as shown in the above table contributes to the improvement in the battery characteristics.

Although electroless plating alone may be considered as a method for plating cadmium onto synthetic resin fibers, in this example, electroless plating was first applied to the fibers, and then electrolytic plating was performed.

Another possibility is to simply perform nickel plating without cadmium plating, but compared to cadmium plating, nickel plating alone has a lower hydrogen overvoltage and poor charging efficiency when charging at low temperatures and high charging rates. Therefore, it is insufficient.

There seems to be a limit to the amount of cadmium plating applied to short fibers. If the upper limit is more than 2 parts by weight, the fiber content will be too large and dispersion will be poor, which is disadvantageous.

Therefore, 0.1 to 2 parts by weight is appropriate.

As described above, the present invention significantly improves the characteristics of the negative electrode by improving the short synthetic resin fibers used as a reinforcing agent in the negative electrode paste and plating the negative electrode surface with cadmium. It is of great value in batteries that use a cadmium negative electrode, especially in batteries that use a sealed cadmium negative electrode.

FIG. 3 is a diagram showing internal pressure characteristics.

A, A'...Invention product, B, B/...
...Conventional product.

Can (Kuben)

Claims (2)

[Claims] (1) Cadmium-plated short synthetic resin fibers are added and dispersed in a paste made by adding a binder to cadmium oxide, and this paste is applied to a porous metal core, followed by cadmium plating. Characteristic manufacturing method of cadmium negative electrode. (2) The method for producing a cadmium negative electrode according to claim 1, wherein the cadmium-plated short synthetic resin fibers are added to the paste in an amount of 0.1 to 2 parts by weight per 100 parts by weight of cadmium oxide.