The positive active-material of lead–acid batteries is lead dioxide. During discharge, part of the material is reduced to lead sulfate; the reaction is reversed on charging. There are three types of positive electrodes: Planté, tubular and flat plates.
Lead–acid batteries were used to supply the filament (heater) voltage, with 2 V common in early vacuum tube (valve) radio receivers. Portable batteries for miners' cap headlamps typically have two or three cells. Lead–acid batteries designed for starting automotive engines are not designed for deep discharge.
In the early days of lead–acid battery manufacture, an electrochemical process was used to form the positive active-material from cast plates of pure lead. Whereas this so-called ‘Planté plate’ is still in demand today for certain battery types, flat and tubular geometries have become the two major designs of positive electrode.
During the past several years extremely corrosion-resistant positive grid materials have been developed for lead acid batteries. These alloys consist of a low calcium content, moderate tin content, and additions of silver. Despite the high corrosion resistance these materials present problems in battery manufacturing.
In a lead-acid cell the active materials are lead dioxide (PbO2) in the positive plate, sponge lead (Pb) in the negative plate, and a solution of sulfuric acid (H2SO4) in water as the electrolyte. The chemical reaction during discharge and recharge is normally written:
This comes to 167 watt-hours per kilogram of reactants, but in practice, a lead–acid cell gives only 30–40 watt-hours per kilogram of battery, due to the mass of the water and other constituent parts. In the fully-charged state, the negative plate consists of lead, and the positive plate is lead dioxide.
The battery is made up of several cells, each of which consists of lead plates immersed in an electrolyte of dilute sulfuric acid. The voltage per cell is typically 2 V to 2.2 V. For a 6 V battery, three cells are connected in series, and for a 12 …