JPH01112660A - Manufacture of cadmium pole for battery - Google Patents

Abstract

PURPOSE:To improve gas absorption characteristics at the time of charging by immersing an electrode mainly consisting of Cd oxide in a plating bath of Ni having a strong acidity so as to form a porous layer of Ni by electrolytic plating on the surface of the electrode. CONSTITUTION:An electrode mainly consisting of Cd oxide is immersed in Ni plating liquid of strong acidity of less than pH2, or preferably less than 1, to perform electrolytic plating. A porous layer of Ni of white without metallic gloss can thus be obtained, having much more of pinholes. A closed type alkali battery is then formed using this Cd pole. Gas absorption characteristics are thus improved, and a rapid charging is enabled.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Applications Prior Art Among various power sources, lead-acid batteries and alkaline batteries are widely used as secondary batteries. Among the latter alkaline storage batteries, the most widely used one is the nickel-cadmium storage battery, and the adoption of a sealed structure was a major factor in expanding the range of practical use.

Furthermore, since a sintered nickel electrode has been developed, it has excellent discharge characteristics, particularly high rate discharge, and has a long life. Furthermore, there is little performance deterioration due to overcharging or neglect, and performance is good even at low temperatures. In addition to these characteristics, it has become possible to seal the device, improving ease of use and reliability.

Since such sealed storage batteries have come to be used in various portable devices, high energy density has been required. This is being addressed by increasing the capacitance density of the electrodes. Recently, there has also been a strong demand for rapid charging.

The principle of sealing a sealed nickel-cadmium storage battery is known as the so-called Neumann method, in which oxygen generated from the nickel electrode is absorbed by the cadmium electrode when charging is complete.
The basic idea is that neither oxygen nor hydrogen is generated by not overcharging the cadmium electrode.

Therefore, in order to enable rapid charging, it is necessary for the cadmium electrode to absorb oxygen gas as quickly as possible. In fact, rapid charging is now possible by, for example, charging a battery for one hour, detecting the completion of charging based on voltage and temperature, and reducing the charging current when the eight overcharged states occur.

Furthermore, to help the reaction of the cadmium electrode with oxygen,
Attempts have been made to add oxygen ionization catalysts such as platinum and palladium, but these are expensive.

It has also been revealed that forming a conductive layer of copper, nickel, or carbon on the surface of the cadmium electrode is also effective.

Problems to be Solved by the Invention Nickel, which has particularly excellent alkali resistance, is preferably used as the conductive porous layer on the surface of the cadmium electrode in order to improve rapid charging characteristics.The method for forming this nickel layer is as follows: The most industrially simple method is electrolytic plating. In other words, when considering electrolyte resistance, oxidation resistance, etc., it is most preferable to form a porous electrolytic nickel plating bath.Therefore, a known nickel plating bath is used, and a cadmium electrode containing mainly cadmium oxide is added to it. When electrolytic plating was performed by dipping after pretreatment, it was possible to form a shiny layer of nickel relatively easily. Using this cadmium electrode, a sealed alkaline storage battery was constructed and the rapid charging characteristics were investigated, and the gas absorption characteristics were also improved. However, to enable high energy density, it is desirable to further improve the gas absorption properties, and it is also desirable to suppress the formation of unnecessary nickel hydroxide during the plating process.

The object of the present invention is to obtain a manufacturing method that can improve the dust absorption characteristics based on the above-mentioned conventional technology.

Means for Solving the Problems The present invention involves adjusting the pH of a known nickel plating bath to 2 or less, preferably 1 or less, and performing electrolytic nickel plating using a cadmium electrode mainly made of cadmium oxide. It is characterized by forming a nickel layer.

Function: In general-purpose nickel plating baths, so-called ordinary baths and double salt baths have a pH of 5.6 to 6.2, W at of 2.
5-5; 2.5-4.5 in bright nickel bath.

When electrolytic plating is performed in such a bath, a nickel layer with few pinholes is formed on the foil, and at the same time, nickel hydroxide is also easily formed.

On the other hand, when electrolytic plating is carried out using sulfuric acid or the like, preferably at pH'l or less, as in the present invention, a white nickel layer is formed with no full gloss, and there are far more pinholes. In other words, it has been found that performing the reverse of so-called normal metal plating is more convenient for gas absorption in sealed alkaline storage batteries. Furthermore, since it is strongly acidic, precipitation of unnecessary nickel hydroxide can be suppressed.

Example Commercially available cadmium oxide was mixed with 3% polyvinyl alcohol (
Make a paste by adding 5% polyethylene fine powder and 0.6% vinyl chloride-acrylonitrile short fibers in one dish. This is 0.15mm thick.

It is applied to a nickel-plated punched metal plate made of iron with a hole diameter of 1.8 mm and a porosity of 50%.

Smooth it through the slit and adjust the thickness to 0.6 mm. Thereafter, it is dried at 120° C. for 2 hours to obtain a paste-type cadmium electrode.

As the battery, a SubC type sealed nickel-cadmium storage battery was used as an example. Therefore, the width of the cadmium pole thus obtained was 3.3 cm.

It was cut to a length of 20 cm, and lead plates were attached to two predetermined locations by spot welding.

The cadmium pole obtained in this way was used as a general-purpose W a
t in a bath (240 g/I of nickel sulfate, 45 g/l of nickel chloride, 30 g/I of boric acid) at 25°C in a bath containing 10 ml of concentrated sulfuric acid (1 liter).
Plating was performed for 2.5 minutes under the condition of A/cm2 using a nickel electrode as a counter electrode.

White nickel plating was uniformly applied to the entire surface of the electrode.

Then, in order to maintain the discharge cuff capacity, the electrode was placed in an electrolytic bath for 2 hours and 4 minutes at a current density of 140 mA/Cm2.
Charging is performed using a nickel plate as a counter electrode in a caustic potassium aqueous solution with a specific gravity of 1.15 at a temperature of 25°C.

This charge amount corresponds to about 16% of the total theoretical cadmium capacity, but since the charging efficiency is low, it can be assumed that about 8% was actually charged.

After washing with water and drying, use commercially available fluorine resin dispersion 2.
A 0-fold diluted solution was added and dried to obtain a cadmium electrode.

As a phase balance for the battery construction, a known foamed nickel electrode was chosen, with a width of 3.3 cm and a length of 17 cm. The thickness is Q, 7 mm. A polyamide nonwoven fabric was used as the separator, and 25 g/I of lithium hydroxide was dissolved in a caustic potassium aqueous solution having a specific gravity of 1.22 as the electrolyte. The nominal capacity is 2.2Ah. This battery is referred to as (A).

Next, for comparison, after sensitizer treatment and activator treatment were performed on the cadmium oxide electrode,
In this case, the same W a t bath mainly containing nickel sulfate, nickel chloride, boric acid, etc. as in (A) was used as it was, and the temperature was 43°C and the TL flow density was 60 mA/e+2 for 6.5 hours.
Electrolytic nickel plating was performed under the following conditions. A battery using the cadmium electrode thus obtained was designated as (B).

The discharge capacities of these batteries during normal charging and discharging were almost the same. For example, at 0.20C charge-0.2C discharge, all showed 2.2 to 2.3Ah.

Next, we investigated the quick charging characteristics of each battery.

In each case, 10 cells were used. The ambient temperature was set to 0° C., and changes in pressure inside the battery were measured when charging at each charging rate. Note that charging was performed at each charging rate up to 1.3 times the discharge capacity. Thereafter, the charge was reduced to 0.20, and the total charge was 1.4 times the discharge capacity.

First, the maximum internal pressure of each battery during IC charging (2, 2A) is 0, 8-0, 9 kg/cm2 for battery (A), 1, 3-1. ,5 kg/cm2
Met.

Next, when it is set to 1.25C (2.75A), battery (A) will have a power of 2.5 to 2.6. (I3) was 3.2 to 3°5.

In other words, the biggest reason why battery (A) was superior in terms of gas absorption compared to battery (B) is that the nickel layer formed on top of cadmium is conductive and has appropriate porosity, that is, pinholes. It seems that this was the case.

As described above, in the battery (A) of the present application, the gas absorption characteristics can be improved by simply making the plating bath strongly acidic.

Effects of the Invention As described above, in the manufacturing method of the present invention, it is possible to improve gas absorption characteristics during charging.

Claims (3)

[Claims] (1) A method for producing a cadmium electrode for a battery, which comprises immersing an electrode mainly made of cadmium oxide in a strongly acidic nickel plating bath, and forming a porous nickel layer on the electrode surface by electrolytic plating. (2) The method for producing a cadmium electrode for a battery according to claim 1, wherein the strong acidity is at least pH 2 or less, preferably pH 1 or less. (3) The method for producing a cadmium electrode for a battery according to claim 1 or 2, which comprises adjusting the pH to 2 or less by adding sulfuric acid or hydrochloric acid.