Hamburg, Germany - A new generation of non-flammable mobile phone batteries could eliminate the hazard of combustion from over-charging, according to a team of German scientists.

They say the novel lithium-ion battery is based on a polymer electrolyte which is non-combustible - unlike the liquid electrolyte in conventional lithium-ion batteries.

Lithium-ion batteries supply the power for cell phones and PDAs, and larger devices such as laptops, cordless screwdrivers and lawnmowers 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 Wuerzburg, Germany, 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 Moeller.

"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 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 parametres 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 Moeller.

A prototype of the new lithium-ion batteries already exists, but between three and five years are likely to elapse before the battery will cross shop counters in laptop computers, PDAs and cordless screwdrivers, 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. (dpa)