Untangling the Structure and Dynamics of Lithium-Rich Anti-Perovskites Envisaged as Solid Electrolytes for Batteries

Abstract

Lithium-rich anti-perovskites (LiRAPs) have attracted a great deal of attention as they have been praised as another superior group of solid electrolytes that can be used to realize all-solid-state batteries free of flammable liquids. Despite several studies that have reported on the properties of LiRAPs, many questions remain unanswered. In particular, these include fundamental ones concerning the structure, stability, and Li-ion conductivity and diffusivity. Moreover, it is not clear whether some of the previously reported compounds do really exist. To untangle the current picture of LiRAPs, we synthesized “Li3OCl” and Li2OHCl polymorphs and applied a wide spectrum of methods, such as powder X-ray diffraction (PXRD), powder neutron diffraction (PND), nuclear magnetic resonance spectroscopy, and impedance spectroscopy to carefully shed some light on LiRAPs. Here we self-critically conclude that the cubic polymorph of the two compounds cannot be easily distinguished by PXRD alone as the lattice metrics an...