January/February 2012
Automation Update

Mystery of lead-acid battery current solved

Chemists have solved the 150-year-old mystery of what gives the lead-acid battery, found under the hood of most cars, its unique ability to deliver a surge of current.

Lead-acid batteries are able to deliver the very large currents needed to start a car engine because of the exceptionally high electrical conductivity of the battery anode material, lead dioxide. A team of researchers have explained for the first time the fundamental reason for the high conductivity of lead dioxide, reports ScienceDaily.

"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 current to be drawn on demand," said Professor Russ Egdell of Oxford University's Department of Chemistry, an author of the paper. "However the origin of conductivity in lead oxide has remained a matter of controversy. Other oxides with the same structure, such as titanium dioxide, are electrical insulators."

Through a combination of computational chemistry and neutron diffraction, the team demonstrated lead dioxide is intrinsically an insulator with a small electronic band gap, but invariably becomes electron rich due to the loss of oxygen from the lattice, causing the material to be transformed from an insulator into a metallic conductor.