More safety for mobile batteries

Tuesday, 06 May, 2008

The safety of lithium-ion batteries has been improved so that in future they could replace motor vehicle lead acid batteries. At the same time, lithium-ion batteries used in computers and other small devices have been made safer following research at the Fraunhofer Institute for Silicate Research ISC in Würzburg.

Lithium-ion batteries have high energy density and voltage (up to 4 V) but at the same time have one big safety disadvantage: the organic electrolytes used in the batteries are inflammable and can easily catch fire. This has already resulted in several fires and subsequent recall campaigns.

“We have succeeded in replacing the inflammable organic electrolytes with a non-flammable polymer that retains its shape,” said ISC team leader Dr Kai-Christian Möller.

“This considerably enhances the safety of lithium-ion batteries. What’s more, because it is a solid substance, the electrolyte cannot leak out of the battery.”

The polymer used by the researchers is derived from the Ormocer group of substances — a compound with silicon-oxygen chains that forms an inorganic structure to which organic side chains become attached.

The big challenge is to ensure that the polymers will efficiently conduct the lithium ions that supply the power for the device being used.

“Normally, the more solid a polymer is, the less conductive it becomes. But we had numerous parameters that we could adjust — for example, we can use coupling elements with two, three or four arms. As a result, we have more possibilities with Ormocer’s than with a single type of plastic,” said Möller.

While a prototype of the new lithium-ion batteries already exists, it will be between three to five years before the battery will cross shop counters in laptop computers, PDAs and cordless screwdrivers, according to experts.

The conductivity of the polymer needs further improvement to enable the battery to deliver or store as much power as possible in as short a time as possible.

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