Li7GeS5Br—An Argyrodite Li-Ion Conductor Prepared by Mechanochemical Synthesis

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 Li 7 GeS 5 Br, which is, to the best of our knowledge, the first compound of the Li 2 S-GeS 2 -LiBr system. Applying combined synchrotron X-ray diffraction and neutron powder diffraction, we show Li 7 GeS 5 Br to crystallize in the F 4̅3 m space group and to be isostructural with argyrodite-type Li 6 PS 5 Br, but with a distinct difference in the S 2- /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-dependen 7 Li 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.