Lithium batteries power cars

Although the lithium-ion cells you see in laptops and mobile phones pack twice as much energy per pound as the next-best kind, they haven't found their way into hybrid cars because they're worryingly prone to fires.

US company, A123Systems claims to have solved the problem with a lithium-ion design using a special formulation for the battery's cathode, or positive plate.

The safety problem that has stood in the way of lithium-ion batteries became notorious last year when laptops using such batteries were shown spouting flames in video clips that circulated on the internet. Millions of lithium-ion batteries had to be recalled, even though no one was hurt. If masses of such batteries had been in automobiles, however, the fires would likely have resulted in the deaths of the passengers.

The fires seem to begin when a small manufacturing defect, perhaps compounded by overcharging, causes oxygen to separate from the compound making up the cathode, a heat-releasing process known as oxidation. As the cell overheats, it can prime oxidation in neighbouring cells, a process known as thermal runaway.

A123 overcame the problem by making its cathodes out of iron phosphate, which bonds to the oxygen more powerfully than the cobalt dioxide found in conventional lithium-ion batteries does.

Its cells are thus far less subject to oxidation, and thus less prone to thermal runaway. The company has minimised iron phosphate's problem of a relatively low operating voltage with a nanopatterning design that improves conductivity in the cathode.

The company's batteries are already in use in other applications demanding a combination of power and safety. The company recently introduced them into a new line of 36 V power tools, twice as powerful as their predecessors.

General Motors has announced that it would use A123's batteries to turn the Chevrolet Volt, now a concept car, into a plug-in hybrid. A plug-in would go considerable distances on battery power alone, usually gaining its charge straight from a wall socket and relying on the gasoline engine only as a range extender.