Li<sub>7</sub>GeS<sub>5</sub>Br—An Argyrodite Li-Ion Conductor Prepared by Mechanochemical Synthesis
Florian Strauss, Tatiana Zinkevich, Sylvio Indris, Torsten Brezesinski
Abstract
In recent years, the search for glassy and ceramic Li+ superionic conductors has received significant attention, mainly due to the renaissance of interest in all-solid-state batteries. Here, we report the mechanochemical synthesis of metastable Li7GeS5Br, which is, to the best of our knowledge, the first compound of the Li2S–GeS2–LiBr system. Applying combined synchrotron X-ray diffraction and neutron powder diffraction, we show Li7GeS5Br to crystallize in the F4̅3m space group and to be isostructural with argyrodite-type Li6PS5Br, but with a distinct difference in the S2–/Br– site disorder (and improved anodic stability). Electrochemical impedance spectroscopy indicates an electrical (ionic) conductivity of 0.63 mS cm–1 at 298 K, with an activation energy for conduction of 0.43 eV. This is supported by temperature-dependent 7Li pulsed-field gradient-nuclear magnetic resonance spectroscopy measurements. Overall, the results demonstrate that novel (metastable) argyrodite-type solid electrolytes can be prepared via mechanochemistry that are not accessible by conventional solid-state synthesis routes.