Improving the Safety of Lithium-ion Batteries

Lithium-ion batteries supply the power for cell phones and PDAs, and larger devices such as laptops are becoming increasingly dependent on this power source. The advantage of these power storage devices lies in their high energy density and voltage (up to four volts). In terms of safety, however, they have one disadvantage - the organic electrolytes are inflammable and can easily catch fire. This has already resulted in several fires and subsequent recall campaigns.

Researchers at the Fraunhofer Institute for Silicate Research ISC in Würzburg say that they have optimized the safety of these batteries.

"We have succeeded in replacing the inflammable organic electrolytes with a non-flammable polymer that retains its shape," says ISC team leader Dr. Kai-Christian Möller. "This considerably enhances the safety of lithium-ion batteries. WhatÃ'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 form 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 cell phone and the PDA.

"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," says Möller.

A prototype of the new lithium-ion batteries already exists, however between 3 and 5 years are likely to elapse before the battery will cross shop counters, the expert believes. 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. Once this happens, though, it is quite realistic to expect this type of battery - in conjunction with a capacitor - to be able to compete with the lead batteries in cars.

Posted to the site on 11th April 2008