"Super-Iron" Comes to the Rescue of Batteries

Scientists have invented a new class of dry batteries--the kind used in flashlights, for example--that have greater capacity and a faster discharge rate than ones on the market today, according to a report in tomorrow's issue of Science.

When a typical battery discharges, electrons absorbed from the electrolyte by the zinc anode pass through an electric circuit and end up in the cathode, where two manganese dioxide (MnO2) molecules join to form a manganese sesquioxide (Mn2O3) molecule, absorbing two electrons in the process. A team led by Stuart Licht at the Technion-Israel Institute of Technology in Haifa has come up with a new cathode made from unusual iron-based molecules--iron(VI), or "super-iron," compounds--that absorb more electrons than manganese dioxide. This larger appetite for electrons translates directly into increased storage capacity: 47% greater than standard manganese dioxide batteries of the same size.

The performance of the super-iron compounds "is very astounding," says Jeff Dahn of Dalhousie University in Halifax, Canada. Denis Dees of Argonne National Laboratory in Illinois says, however, that he would like to see evidence that the new batteries can survive for 6 to 12 months on the shelf and still be discharged. Because of the questionable stability of iron(VI) compounds, he says, "it is interesting that they have made it work at all."

Licht's team is now studying cathodes made from mixtures of super-iron compounds to boost performance and improve their rechargeability. "This avenue looks very hopeful," he says.