LiGeSBr-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 LiGeSBr, which is, to the best of our knowledge, the first compound of the LiS-GeS-LiBr system. Applying combined synchrotron X-ray diffraction and neutron powder diffraction, we show LiGeSBr to crystallize in the 4̅3 space group and to be isostructural with argyrodite-type LiPSBr, but with a distinct difference in the S/Br site disorder (and improved anodic stability). Electrochemical impedance spectroscopy indicates an electrical (ionic) conductivity of 0.63 mS cm at 298 K, with an activation energy for conduction of 0.43 eV. This is supported by temperature-dependent 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.