23 January 2008

Germans developing battery
that never needs recharging

Tired of mobile phones that always need recharging at the worst possible moment?!? Researchers in Germany are developing a revolutionary new battery that never needs recharging!?

Mobile phones, notebook computers and iPods are all devices dependent on rechargeable lithium-ion batteries to deliver power.

But the German researchers have developed a new class of inorganic ionic conductor with a structure analogous to that of the mineral argyrodite.

A team led by Hans-Joerg Deiseroth in Siegen, Germany, reports in the journal Angewandte Chemie the characterization of the most conductive representative of the man-made argyrodite minerals made of lithium, phosphorus, sulphur and bromine atoms.

In ionic conductors, charge is not transported in the form of electrons as it is in metals. Instead, the charge is transported in the form of charged particles typically, lithium ions.

This transport requires materials in which the lithium ions can move as freely as possible. The team from the University of Siegen, in cooperation with scientists at the University of Muenster, started from a long-known mineral: argyrodite is a silver, germanium and sulphur-containing mineral discovered near Freiberg, Germany, in 1885 and the silver ions in this material are very mobile.

The individual components of argyrodite can be replaced by a number of other atoms without altering the typical structure of the mineral, according to a report on the physorg.com website.

The term argyrodite now refers to an entire class of compounds that have a specific arrangement of atoms and type of structure.

The team led by Deiseroth produced a version of the mineral in which silver is replaced by lithium, germanium by phosphorus, and some of the sulphur atoms by halides (chloride, bromide or iodide), resulting in argyrodite-like structures.

In the crystal lattice the phosphorus, sulphur and halide atoms adopt a dense tetrahedral packing arrangement in which the gaps are filled somewhat regularly with lithium ions.

The lithium ions can "jump" from gap to gap, said the report by physorg.com. The freely-moving ions indicate that the solid has a high ionic conductivity and the reported bromine-containing structure has the highest ionic conductivity of lithium ions known for any argyrodite to date.

The scientists have thoroughly examined the lithium argyrodites by single-crystal X-ray crystallography and nuclear magnetic resonance spectroscopy.