Oxide corrosion products in lead acid battery plates

What is it about?

The article determines the progressive changes in the crystal structure of PbO during its transformation from a tetragonal form at room temperature, to a lower symmetry (monoclinic) form at high temperature. A total of 20 neutron powder diffraction data sets were collected at the ILL, France, over the temperature range 295 K to 925 K. The transformation between the two phases commences at around 850 K through a rapid expansion of the c-axis and an increase in the displacement parameter of the O atom, as the forerunner to Pb-O bond-breakage and the movement of the O atoms by 1.2 angstroms. The Pb atoms move by only about 0.2 angstroms during this process but the combination of O and Pb atomic movements results in the formation of a non-crystalline intermediary phase from which the high temperature form emerges. As a result of these changes, the flat O layers in the low temperature phase split into two heavily corrugated O layers sandwiched between the relatively immobile Pb atom layers, held together by van der Waals forces between the lone electron pairs on the Pb atoms..

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Why is it important?

Corrosion of the lead electrodes in lead-acid batteries is associated with reduced performance and shorter cycle life of these batteries. The article seeks to understand the nature of the transformation between the room temperature form of lead monoxide (litharge) and the high temperature form (massicot). In so doing, the article also sheds light on the crystal structures of the so-called 'intermediate' oxides of lead, with stoichiometry between PbO and Pb3O4 which are also involved in the corrosion.

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