New class of lithium-rich solids with unusually high lithium mobility.
Mobile phones, notebook computers, iPods - the
boom in portable computing and communications devices is dependent on
rechargeable lithium-ion batteries to deliver power. These batteries
offer the highest energy density, allow laptops to function for useful
amounts of time, and do not display a memory effect when compared to
other types of rechargeable batteries. However, modern rechargeable
batteries are still not truly satisfactory. Modern, efficient,
rechargeable batteries and fuel cells require materials with an enhanced
ability to conduct lithium ions. German researchers have now developed a
new class of inorganic ionic conductor with a structure analogous to
that of the mineral argyrodite. A team led by Hans-J�rg 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, sulfur, 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 M�nster,
started from a long-known mineral: argyrodite is a silver-,
germanium-, and sulfur-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. 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 sulfur
atoms by halides (chloride, bromide, or iodide), resulting in
argyrodite-like structures that have a composition of Li6PS5X
(X: Cl-, Br-, or I-).
In the crystal lattice the phosphorus, sulfur, and halide atoms adopt
a dense tetrahedral packing arrangment in which the gaps are filled
somewhat regularly with lithium ions. The lithium ions can �jump� from
gap to gap. 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. This analysis allowed precise characterization of the
crystal structures of these compounds and provided fascinating
insights into the dynamics of the mobile lithium ions.
Further Information
and Source:
-
Hans-J�rg Deiseroth, Prof. Dr., Shiao-Tong Kong, M.Sc., Hellmut
Eckert, Prof. Dr., Julia Vannahme, Dr., Christof Reiner, Dr.,
Torsten Zai�, Dr., Marc Schlosser, Dr.: Li6PS5X: A Class of Crystalline Li-Rich
Solids With an Unusually High Li+ Mobility.
In: Angewandte Chemie International Edition; 2008, 47,
755�758; published Online: 27 Dec 2007;
DOI 10.1002/anie.200703900.
