This finding explains why these batteries are able to deliver a surge of current when the car is started.
Lead oxide, the battery anode material of lead-acid batteries, allows them to deliver the very large currents that are required to start a car. This is due to the extremely high electrical conductivity of lead oxide. Neutron diffraction studies, along with computational chemistry, have enabled scientists, for the first time, to gain a fundamental understanding of the unique properties of lead oxide.
" The unique ability of lead acid batteries to deliver surge currents in excess of 100 amps to turn over a starter motor in an automobile depends critically on the fact that the lead dioxide, which stores the chemical energy in the battery anode, has a very high electrical conductivity, thus allowing large currents to be drawn on demand,” said Professor Russ Egdell of Oxford University’s Department of Chemistry. “However the origin of conductivity in lead oxide has remained a matter of controversy ”.
Professor Egdell and his group initially became interested in lead oxide when they began to question what it is that makes it a metallic conductor. It was a fascinating area of study because the other oxides in the same group of the periodic table, such as titanium oxide, are all insulators.
Using theoretical calculations, the group were able to show that oxygen vacancies can form very easily in lead oxide. The calculations further revealed that oxygen vacancies give metallic behaviour by freeing up electrons to carry electrical current. Neutron diffraction completed the jigsaw by providing experimental evidence that commercial lead oxide powder is oxygen- deficient by showing that oxygen sites were 1.6% vacant.
" The work demonstrates the power of combining predictive materials modelling with state-of-the-art experimental measurements ” said Professor Egdell.
Working with a team of researchers from Oxford University, the University of Bath and Trinity College Dublin, ISIS has helped to reveal what makes lead oxide such a powerful electrical conductor. This insightful revelation has enabled scientists to understand more about lead oxide at the fundamental level. The techniques developed to solve this problem will be used for predicting material properties for other applications.
Professor Russell Egdell, University of Oxford
Research date: February 2012
Phys. Rev. Lett. 107, 246402 (2011) [5 pages]
Nature of the Band Gap and Origin of the Conductivity of PbO2 Revealed by Theory and Experiment
David O. Scanlon, Aoife B. Kehoe, Graeme W. Watson , Martin O. Jones, William I. F. David, David J. Payne, Russell G. Egdell, Peter P. Edwards, Aron Walsh