Lead Electroplating onto Copper

Testing full sized batteries for lead (and antimony) electroplating can be a needlessly expensive and tedious procedure. Fortunately, it is possible to speed up and to scale down the process experimentally and to provide a result within 24 hours using easily obtainable materials and inexpensive test gear.

An example of one such experiment has been photographed at one picture frame every 2 minutes and converted into a short movie which can be viewed from this web site.

The test cell  consists of a glass beaker filled with ordinary battery acid. The positive electrodes are sections carefully dissected from a regular motive power positive battery plate and are charged ahead of the experiment. The negative electrode consists of a short length of copper wire. Copper typically reacts minimally with lead-acid functioning as long as a charging current is maintained.

The copper negative electrode wire is located at the center of the beaker, flanked by two lead-acid type positive electrodes. Hydrogen gas evolves as result of electrolysis. The copper tint of the negative electrode can be seen darkening progressively.

The end-of-plating potential, shown at 2.62 volts, corresponds to a typical end-of-charge potential for a conventional lead-acid motive power battery cell. Upon switching off the current, the test cell potential initially falls rapidly before steadying to a more gradual decline from around 2.25 - 2.24 volts, suggesting yet another aspect the test cell has in common with a conventional lead-acid cell. In the absence of lead on the negative, the potential would fall instantly to 1.5V.

Anticipating a comparatively small A-H capacity, a 10 K-ohm resistor is connected across the test cell. Ten minutes into the discharge the cell potential has fallen to 2.03 volts. The electrode grows lighter, implying a conversion from lead to lead sulfate.

Every measurement and observation appears to confirm a conventional lead-acid pattern, hence it can be accepted that the on-plated material at the negative electrode is, indeed, lead metal, the dark appearance confirming the presence also of antimony.

TEST EQUIPMENT:

Regulated power supply, 0 – 20 V, constant voltage controlled;
                                              0 – 1 A, constant current controlled;
Power supply setting: 60 milliamps, constant current;
Digital multimeter, 2½ digits, used to measure cell voltage;
Moving coil multimeter, used to measure charge and discharge current;
10 K-ohm, ½ watt resistor, to provide discharge load.