Nuts and Volts - February 2012

FIGURE 4. Disassembled NiCad.

1. Cathode plate. 2. Separator.

3. Anode plate.

homebrewed cell was to literally use a conductive glue to attach the oxides to the outside of the electrodes. This gives a very high surface area “sandpaper” like finish to the electrodes, which is exactly what we want.

The electrodes themselves need to be nickel, or nickel plated. It’s very important to remember in your own designs that virtually any material other than nickel will corrode rapidly in this type of cell under the electrical action. If you’d like to do your own nickel plating, Sources are included here.

Your plate size can be anywhere from 10 cm square to a little over 50 cm square and still fit easily in a mason jar. It is certainly possible to greatly increase this size with multiple plates or even a standard “jelly roll” battery construction. Figure 4 shows this jelly roll construction of a NiCad battery.

Of course, your plates must not touch each other in the cell, so you may need to use a permeable nonconductive separator. This is actually a big topic, but for an experimental cell, it’s possible to use layers of fiberglass screen (available at any hardware store).

For my own simple cells (pictured), I soldered some solid copper wire to a fine copper screen (I think copper foil or plate would work, as well). I coated the solder connection with epoxy, and then nickel plated the screen.

Next, I simply coated the screen with a very thin layer of conductive epoxy (it goes a VERY long way if spread thin). (Conductive epoxy can be found in both nickel bearing and silver bearing.)

Last, I sprinkled and pressed powdered nickel oxide into the wet glue for my positive plate, and iron oxide for my negative plate. The results can be seen in Figure 5.

Though I’m not certain what the actual longevity of using epoxy to hold oxides to the plates will be, my test cells are now more than a year old and have been charged daily from solar cells without problems. So, mark this method as seems to work but, of course, is still experimental.

Begin by mixing a 20% solution (by weight) of potassium hydroxide and distilled water in a pyrex beaker. Keep in mind while doing so that potassium hydroxide should be added slowly to the water; never the other way around. Potassium hydroxide will react exothermically and some heat will be generated.