Phase evolution during lithium–indium halide superionic conductor dehydration

Select rare-earth alkali halides have demonstrated high lithium ion conductivity. The conductivity appears to be related to the stability of the crystal phase, ordering of the lithium sublattice and the amount of residual H2O. Li3InCl6 can be synthesized from concentrated aqueous solution through controlled dehydration. In this work, we track Li3InCl6 dehydration using a multimodal approach that combines thermogravimetric, spectroscopic, X-ray diffraction, and neutron scattering techniques. In situ X-ray diffraction suggests a single phase transition caused by dehydration, in disagreement with spectroscopic and thermodynamic measurements. Neutron scattering, being sensitive toward the H2O and Li sublattices, reveals multiple phase transitions. We show that the loss of the final trace H2O leads to strain and grain boundary formation. Thus, controlled dehydration may be a viable strategy for high-throughput processing for roll-to-roll manufacturing of REAH solid electrolytes.