An accumulator in which the electrodes are made of lead and the electrolyte consists of dilute sulphuric acid. The electrodes are usually cast from a lead alloy containing 7–12% of antimony (to give increased hardness and corrosion resistance) and a small amount of tin (for better casting properties). The electrodes are coated with a paste of lead(II) oxide (PbO) and finely divided lead; after insertion into the electrolyte a ‘forming’ current is passed through the cell to convert the PbO on the negative plate into a sponge of finely divided lead. On the positive plate the PbO is converted to lead(IV) oxide (PbO2). The equation for the overall reaction during discharge is:PbO2+2H2SO4+Pb → 2PbSO4+2H2O The reaction is reversed during charging. Each cell gives an e.m.f. of about 2 volts and in motor vehicles a 12-volt battery of six cells is usually used. The lead-acid battery produces 80–120 kJ per kilogram. Compare nickel-iron accumulator.
PbO2+2H2SO4+Pb → 2PbSO4+2H2O
Subjects: Chemistry — Physics.