Exploring Aliovalent Substitutions in the Lithium Halide Superionic Conductor Li <sub> 3– <i>x</i> </sub> In <sub> 1– <i>x</i> </sub> Zr <sub> <i>x</i> </sub> Cl <sub>6</sub> (0 ≤ <i>x</i> ≤ 0.5)
Bianca Helm, Roman Schlem, Björn Wankmiller, Ananya Banik, Ajay Gautam, Justine Ruhl, Cheng Li, Michael Ryan Hansen, Wolfgang G. Zeier
Abstract
In recent years, ternary halides Li3MX6 (M = Y, Er, In; X = Cl, Br, I) have garnered attention as solid electrolytes due to their wide electrochemical stability window and favorable room-temperature conductivities. In this material class, the influences of iso- or aliovalent substitutions are so far rarely studied in depth, despite this being a common tool for correlating structure and transport properties. In this work, we investigate the impact of Zr substitution on the structure and ionic conductivity of Li3InCl6 (Li3–xIn1–xZrxCl6 with 0 ≤ x ≤ 0.5) using a combination of neutron diffraction, nuclear magnetic resonance, and impedance spectroscopy. The analysis of high-resolution diffraction data shows the presence of an additional tetrahedrally coordinated lithium position together with a cation-site disorder, both of which have not been reported previously for Li3InCl6. This Li+ position and cation disorder lead to the formation of a three-dimensional lithium-ion diffusion channel, instead of the expected two-dimensional diffusion. Upon Zr4+ substitution, the structure exhibits nonuniform volume changes along with an increasing number of vacancies, all of which lead to increasing ionic conductivity in this series of solid solutions.