JPS6329446A - Fmanufacture of cadmium electrode for cell - Google Patents

Abstract

PURPOSE:To improve the conductivity and the utilization rate, and to realize a long service life, by soaking an electrode in a specific activator solution, and then giving a electroless plating. CONSTITUTION:After a paste type cadmium electrode is processed in a comercial synthesizer, it is soaked in an activator solution diluted eight times by methanol. After being soaked about two min, it is dried up. Then a copper plating is given in a copper electroless plating solution. As a result, a cell cadmium of an excellent conductivity, a high utilization rate, and a long service life can be produced.

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.

With the development of sintered electrodes, this nickel-cadmium storage battery has been able to significantly improve its charge/discharge characteristics, lifespan, and low-temperature characteristics, and the adoption of a sealed type has improved handling.

However, although efforts are being made to improve energy density and reduce costs, they are 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 type instead of a sintered type has made it possible to reduce costs to some extent, but the current situation is that the utilization rate of cadmium has not been sufficiently improved.

As a means to improve the utilization rate of such cadmium electrodes, we proposed and made it 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. Further, as the cadmium active material, there are metal cadmium, cadmium oxide, cadmium hydroxide, and other cadmium compounds, but in consideration of economical efficiency and filling property into the electrode, a material composition mainly composed of cadmium oxide is most preferable.

Problems to be Solved by the Invention It has been revealed that forming a conductive and porous layer on the surface of a cadmium active material is highly effective in improving the utilization rate and lifespan of cadmium electrodes for alkaline batteries. Cadmium oxide is a promising material for the cadmium active material, and the surface layer is preferably formed by electroless plating to form a copper or Niacel layer. However, when electroless plating is applied to cadmium oxide by a conventionally known method, part of the cadmium oxide is converted to cadmium hydroxide during this process. Still, electroless plating is possible, but when making a paste-type cadmium electrode, it is preferable to use a large amount of cadmium oxide, which has a large apparent specific gravity, in order to increase the filling amount. Furthermore, when the base material, cadmium oxide, changes to cadmium hydroxide during the plating process, the adhesion strength of the plate appears to be weak. Therefore,
It is better to prevent cadmium oxide from converting into cadmium hydroxide during the electroless plating process as much as possible.

In addition, when performing electroless plating after electrode manufacturing, if a so-called paste-type electrode is used, which uses a binder that is most suitable for mass production, the electrode has water repellency, so it is better to use a conventional aqueous solution. It was difficult to achieve uniform plating with electroless plating using .

Means to Solve the Problem Generally, the electroless plating process is as follows: (1) Synthetizer liquid immersion - (Water washing) - Activator liquid immersion - (Water washing) - Electroless plating liquid immersion - Washing - Drying. Also, depending on the case, the synthesizer liquid immersion may be omitted.

In the present invention, during these steps, as an activator liquid,
Water-compatible solvents, such as methanol, ethanol, acetone, in conventional aqueous solutions.

Add ethylene glycol, fluoropylene gelylcol, etc. This allows the subsequent electroless plating to be performed while suppressing the change from cadmium oxide to cadmium hydroxide that occurs during the plating process. Furthermore, among these solvents, solvents that reduce the surface tension of aqueous solutions, such as methanol and acetone, are particularly effective, and their addition makes it possible to improve wetting of the paste-type electrode and make the activator treatment uniform. It is something to do.

Regarding the amount of these solvents to be added, for example, commercially available activator liquids are generally used after being diluted several times with water, so it is sufficient to use a solvent that is compatible with water.

Function: When electrolessly plating copper or nickel on cadmium oxide powder or a cadmium electrode mainly made of cadmium oxide, the activator liquid used in the plating process contains
Add a solvent compatible with water.

The cadmium electrode obtained by this method has a larger capacitance per unit as a cadmium electrode for batteries than that obtained by simply activating it with an aqueous solution and then electroless plating, and has a longer lifespan. be.

Further, even when performing electroless plating after manufacturing the electrode, the activator is uniformly impregnated into the electrode, so that subsequent electroless plating is performed not only on the surface but also inside the electrode. Therefore, it is highly effective in improving the utilization rate of cadmium and extending its life.

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, the plating was performed after the electrode was created.

Without any problem, mix commercially available cadmium oxide with 3% polyvinyl alcohol and 2% ethylene glycol solution, 2% polyethylene fine powder of 5% by weight, and 0.6% vinyl chloride-acrylonitrile short fibers, etc., and make a paste. to make. This has a thickness of 0.15 cm, a hole diameter of 1.8 mR1, an opening degree of 50%
A nickel-plated punched iron plate is applied to both sides as a core material, smoothed through slits, and adjusted to a thickness of 0.6 mm. Thereafter, it was dried at 120° C. for 2 hours to obtain a paste-type cadmium electrode.

Thereafter, this paste-type cadmium electrode was electrolessly plated with copper. First, after performing a commercially available synthesizer treatment, the activator solution was immersed in a solution diluted 8 times with methanol. After immersion for 2 minutes, this was dried at 60° C. for 16 minutes, and then copper plating was performed using a commercially available copper electroless plating solution. At this time, the size of the electrodes is equivalent to 10 AA size sheets, and the activator liquid is 10
Using CC, 70 CC of methanol was added to this. The electrode was immersed in this solution. As the copper plating solution, 100 cc of a commercially available plating solution was used, which was diluted with 500 cc of water. Plating was carried out at 40°C for 15 minutes. Thereafter, it was washed with running water at room temperature for 20 minutes, replaced with acetone, and then dried at 80°C. The weight increase due to this treatment was 0.ss% compared to cadmium oxide. A battery using the cadmium electrode thus obtained was designated as A.

Next, for comparison, a battery using a cadmium electrode obtained in the same process as battery A was added as battery B using only water as the activator solution before electroless copper plating of a paste-type cadmium electrode.

First, before comparing the characteristics of batteries A and B, the utilization rates of the cadmium electrodes used in batteries A and B were determined.

In other words, a test battery was constructed using a nickel electrode with a sufficiently large capacity to comply with the cadmium pole rule, but an electrolytic solution having the same composition as batteries A and B was sufficiently used, and the test was conducted in an open type. Charge at 25℃, 0. IC 14 hours, discharge 25℃, 0.2C1
Conditions were used where the terminal voltage was up to 0.8V.

As a result, in one cycle of discharge, the cadmium electrode of battery A has a capacity of 385 m equivalent to 1 g of cadmium oxide.
Ah, 373 nnAh in B, 325 after adding cadmium oxide that has not been subjected to 7-day sowing.
It was mAh. Also, just to be sure, charging and discharging were repeated under these conditions, and after 20 cycles, the results were 370 mAh for A, 359 mAh for B, and 251 mAh without plating. In other words, it can be seen that A of the present invention has the best utilization rate and life.

Next, the characteristics of batteries A and B were compared.

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

This was partially charged in advance for 9 minutes under the conditions of a current of 1oA and an aqueous caustic potash solution with a specific gravity of 1.16, washed with water, and dried. As a counterpart electrode, a known high capacity sintered nickel electrode was selected, with a width of 39 mm and a length of 220 mm. In this case as well, lead plates were attached at two locations.

A polyamide nonwoven fabric was used as the separator, and 25 i/l of lithium hydroxide was dissolved in a caustic potassium aqueous solution with a specific gravity of 1.18 as the electrolyte. This battery is called A. The nominal capacity is 2.4 sAh.

First, each battery was charged at 0.10 for 14 hours, and the standard capacity was determined at 0.20 discharge. In both cases, the capacity is 2.46 Ah as described above, and the discharge ends at the nickel positive electrode. Therefore, it seems that there is not much difference in such normal charging and discharging.

However, next we investigated the rapid charging characteristics. 10 at 0℃
When charging was performed for 1.5 hours and the internal pressure of the battery was determined, battery A had a maximum of 3.1 and 9/-1 battery B had a maximum of 3.1. sK9/
ffl had a slightly better A. This seems to be because A has a better charging/discharging efficiency than B, and A has slightly more cadmium required during charging than B. next,
When a 12C discharge was performed, at 35℃, both
．． C) Shows 1Ah. However, battery A is 0.02
The average value of V is high, and this is probably because the copper plating on the cadmium is strong, so the conductivity is even slightly better.

In addition, as a life test, we selected harsh conditions for cadmium negative electrodes, including charging at a rate of 10 hours at 0°C and discharging at 26°C for 50 cycles. becomes larger, so
Along with the cycle, it becomes the cadmium law. In A, 15
Even after 0 cycles, the nickel polar law was observed, but in B, 1
The cadmium extreme law was reached after 15 cycles. Therefore, in order to avoid the cadmium polarity rule in B, it is necessary to increase the capacity of the negative electrode, and the discharge capacity of the battery will decrease accordingly. This phenomenon is also due to the fact that the cadmium electrode of battery A is superior to battery B in terms of charging and discharging efficiency.

Effects of the Invention By using a cadmium electrode that is plated after immersing the electrode in an activator solution containing a solvent that is compatible with water, it is possible to provide cadmium for batteries with excellent conductivity, high utilization rate, and long life. can.

Claims (4)

[Claims] (1) A method for producing a cadmium electrode for a battery, which comprises immersing the electrode in an activator solution containing a solvent that is compatible with water, and then performing electroless plating. (2) According to claim 1, the electrode is formed by using cadmium oxide powder, immersing it in an activator solution containing a solvent that is compatible with water, and then performing electroless plating. A method for manufacturing cadmium electrodes for batteries. (3) Claim 1, characterized in that a cadmium electrode containing mainly cadmium oxide and a binder is immersed in an activator solution containing a solvent that is compatible with water, and then electroless plating is performed. The method for manufacturing the described cadmium electrode for batteries. (4) The method for producing a cadmium electrode for a battery according to any one of claims 1 to 3, wherein the electroless plating is copper or nickel.