JPS6334852A - Cadmium electrode for cell - Google Patents

Abstract

PURPOSE:To improve the durability of copper itself so as to realize a long life time and to suppress the self-discharge by applying nickel plating additionally on copper plating. CONSTITUTION:A paste type cadmium electrode is constructed by coating a paste made by adding specified substance to cadmium oxide on the both side surfaces of a core material made of nickel plated iron punching plate, and smoothing and drying it. Then copper plating is applied to this cadmium electrode by electroless plating in a electroless bath. Then nickel plating is applied to the said electrode by electrolytic plating using nickel watt bath. Further. the electrode is washed with flowing water of normal temperature, substituted by aceton and dried.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to improvements in cadmium electrodes for alkaline storage batteries.

BACKGROUND OF THE INVENTION As is well known, storage batteries used as various power sources include lead-acid batteries and alkaline batteries. A typical alkaline battery system is a nickel-cadmium storage battery.

The development of sintered electrodes made it possible to significantly improve the charging/discharging characteristics, lifespan, and low-temperature characteristics of this nickel-cadmium storage battery, and the use of a sealed type improved handling.

However, although efforts are being made to improve energy density and reduce costs, they are still not sufficient. For example, in order to improve energy density, foamed electrodes have been developed for nickel electrodes, but it cannot be said that sufficient cost reduction has been achieved. On the other hand, with regard to cadmium electrodes, the development and commercialization of a paste method instead of a sintering method has made it possible to reduce costs slightly;
At present, the improvement in the utilization rate of cadmium is not sufficient.

As a means to improve the utilization rate of such cadmium electrodes, it has been proposed and made possible to form a conductive and porous layer on the surface of the cadmium active material. Electroless plating is the simplest and most industrial method for forming a porous layer on the surface. Examples of the cadmium active material include metal cadmium, cadmium oxide, cadmium hydroxide, and other cadmium compounds; however, in consideration of economical efficiency and ability to fill electrodes, a material composition mainly composed of cadmium oxide is most preferable.

Problems to be Solved by the Invention It has been found that forming a conductive and porous layer on the surface of a cadmium active material has a great effect on improving the utilization rate and life of cadmium electrodes for alkaline batteries. It was found that cadmium oxide is a promising material for the cadmium active material, and that it is preferable to form a copper or nickel layer by electroless plating to form the surface layer.

It has now become clear that plating with such metals is effective in improving the utilization rate of cadmium and suppressing the deterioration of cadmium electrode performance due to repeated charging and discharging, in other words, extending the life of the electrode.

However, when copper is used as a metal, it is difficult to use it under harsher conditions than normal use, such as long-term storage rather than charge-discharge cycles, high-temperature charging/discharging, and over-discharging. Under certain conditions, copper may corrode or dissolve, causing the formation effect to be lost.

On the other hand, when nickel is used, there is almost no such interlayer, but if nickel is in direct contact with cadmium, there is a problem that self-discharge of cadmium is somewhat accelerated. This is because cadmium in contact with nickel reacts with the electrolyte due to the difference in hydrogen overvoltage, generating hydrogen and oxidizing the cadmium.

Means for Solving the Problems Therefore, the present invention proposes that the cadmium surface of the cadmium electrode is first plated with copper, and then plated with nickel.

Both copper plating and nickel plating are electroless.

There are both electrolytic plating methods, but the former method is used for copper because electroless plating is easier, and the latter method is used for nickel because electrolytic plating is superior in terms of uniformity. is one effective means.

Therefore, copper plating may be performed by plating the cadmium electrode, for example, cadmium oxide powder, or after the cadmium electrode is manufactured, but it is better to perform the 217 Kel plating in the form of an electrode. In addition, when using cadmium oxide as a starting material, in order to suppress the conversion to cadmium hydroxide as much as possible, methanol, which is a water-compatible solvent, is added to the bath for each plating during the plating process.
Adding ethanol, acetone, ethylene glycol, etc. is an effective method.

Function: By first coating the cadmium electrode with porous copper and then coating it with porous nickel, the durability of the copper itself is improved, and since nickel is inherently durable, it has a long life. This makes it possible to improve the utilization rate of cadmium, and also greatly solves the problem of self-discharge caused by cadmium coming into direct contact with nickel.

EXAMPLE The present invention will be described in detail by taking as an example one example in which the present invention exhibits the greatest effect, which is the plating of paste-type cadmium electrodes. In this example, plating is performed after electrode creation. First, commercially available cadmium oxide was mixed with polyvinyl alcohol at a 6% by weight ratio of 3 wt% ethylene glycol solution.
of polyethylene fine powder, also 0.6 inch of vinyl chloride.
Make a paste by adding acrylonitrile copolymer short fibers to a thickness of 0.15 mm.

A nickel-plated bunching board made of iron with a hole diameter of 1.8 m and a porosity of 50% is applied as a core material to both sides, smoothed through a slit, and adjusted to a thickness of 0.6.

Thereafter, it was dried at 120° C. for 2 hours to obtain a paste-type cadmium electrode.

After that, this paste-type cadmium electrode was electrolessly plated with copper. First, a commercially available synthesizer treatment was performed;
After that, the activator solution was immersed in a bath in which the activator solution was diluted 6 times with methanol. After immersion for 2 minutes, this was dried at 60° C. for 15 minutes, and then copper plating was performed using a commercially available copper electroless plating bath. At this time, the electrodes used are equivalent to 10 AA size electrodes, and the activator liquid was 8CC.
40 cc of methanol was added to this. The electrodes were immersed in this bath. As the copper plating bath, 70 cc of a commercially available plating bath was used, which was diluted with 400 cc of water. Plating was carried out at 40°C for 16 minutes. Afterwards, rinse with running water at room temperature for 10 minutes, replace with acetone, and then use at 80°C.
It was dried. The weight increase due to this treatment was 0.5% compared to cadmium oxide.

Then, using a known 2" Kelwatt bath at 40°C.

Electrolytic plating of nickel was carried out under the conditions of current density 20 rnA/M * time 20 minutes. Thereafter, it was similarly washed with running water at room temperature for 20 minutes, replaced with acetone, and then dried at 8 °C. The weight increase due to this treatment was about 1.6 inches relative to cadmium oxide.

As an example of a battery, a AA sealed nickel-cadmium storage battery was used. Therefore, the cadmium electrode thus obtained was cut to a width of 39 m and a length of 261 m, and lead plates were attached to two predetermined locations by spot welding.

This was partially charged in advance for 9 minutes under the conditions of a current of 10 A and a caustic aqueous solution with a specific gravity of 1.15, washed with water, and dried.

As a mating electrode, a known high-capacity sintered two-sokel electrode was selected, also having a width of 39 mm and a length of 220 mm. In this case as well, a polyamide nonwoven fabric was used as the 0 separator with lead plates attached at two places, and as the electrolytic solution, 2 tsq/l of lithium hydroxide was dissolved in a caustic potassium aqueous solution with a specific gravity of 1.18. This battery is called A.

Its nominal capacity is 2.45 Ah.

Next, for comparison, a battery using a cadmium electrode obtained by coating only copper by electroless plating was added as B. In this case, the weight increase due to copper was set to 2.0%. 1. The same cadmium electrode as A and B was charged to cadmium, and a battery using a cadmium electrode electrolytically plated with nickel was added as C. In this case as well, the weight increase due to plating was 2.0%.

First, we investigated the utilization rate of the cadmium electrode itself used in these batteries A-C, and found that charging was at 26°C and 0.1C for 14 hours, and discharging was also at 25°C and 0.30%, and the cadmium pole rule of nickel Terminal voltage O, SV of cadmium test battery
The conditions were set up to. The capacity density when discharging immediately after charging was 380 rnA h /CI. However, 0. When I charged it with IC and left it for 25 days and then discharged it with O and AC in the same way, the capacity decreased by 5.5% for A and 3.2ch for B, but about 10% for C. There was a decline. In other words, in terms of self-discharge, C, which had nickel plating directly on the cadmium electrode, was inferior. Similarly, charging at 25°C was 0. The IC was used for 14 hours, and the discharge was carried out at 26° C., the same as 0.30V, but with the terminal voltage up to 10.2V. As a result, in the 2Q cycle, while A was 356 mAh and C was 349 mAl1, it decreased to 315 mAh in B, and oxidation and partial peeling of the copper plating were observed. In other words, under such severe usage conditions, applying nickel plating on top of copper plating has a greater effect on suppressing performance deterioration than simple copper plating.

After performing such evaluation, the characteristics of batteries A and B were investigated. That is, during normal repeated charging and discharging, there were no problems in discharge performance or lifespan, not only in the present invention but also in the comparative example.

However, after charging for 14 hours at 40℃ at 1C, 45
When the battery was left for 3 months at 40°C and then charged and discharged at 40°C and 0.20°C, oxidation and dissolution of the copper coating layer was observed, especially under conditions where the final discharge voltage was OV.

Effects of the Invention By applying copper plating on top of cadmium and then nickel plating on top of cadmium with cadmium active material powder or after electrode formation, we have created a cadmium electrode for batteries that has a long life, high utilization rate, and low self-discharge. can be provided.

Claims (3)

[Claims] (1) A cadmium electrode for batteries characterized by further applying nickel plating on top of copper plating. (2) The cadmium electrode for a battery according to claim 1, wherein the copper plating is formed by electroless plating and the nickel plating is formed by electrolytic plating. (3) Claim 1, in which a porous layer of copper is formed by electroless plating on a cadmium electrode mainly consisting of cadmium oxide and a binder, and a porous layer of nickel is formed thereon by electrolytic plating. Cadmium poles for the batteries listed.