Mechanism of formation of dense anodic films of PbO on lead and lead alloys in sulfuric acid - Use of an O-18 tracer

In order to elucidate the growth mechanism of the passive alpha-PbO at the interface grid/positive active material of the lead-acid batteries, a seque ntial electrochemical method using O-18 was set up. Tt was established that the formation of a thick, dense PbO layer on pure lead and lead alloys (Pb -Sb, Pb-Ca-Sn), in potential conditions simulating deep discharged batterie s for electric vehicles, is the consequence of a solid-state process, with O2- as the predominant diffusing species. Diffusion of O2- anions occurs al ong the grain boundaries of PbO, as well as in the grain bulk, probably bet ween the two neighboring planes of Pb2+ cations of the PbO tetragonal struc ture. (C) 1999 The Electrochemical Society. S0013-4651(98)04-058-0. All rig hts reserved.