Exploring Dehydration Mechanisms and Conductivity Optimization in Li₃InCl₆●xH₂O via In Situ Synchrotron Techniques

In recent years, halide solid electrolytes have attracted widespread attention due to their high ionic conductivity, high oxidative stability, and diverse synthesis methods. Among these methods, water-mediated synthesis is the most environmentally friendly and cost-effective approach. The ion conductivity of lithium indium chloride (Li₃InCl₆, LIC) is strongly influenced by the synthesis conditions, particularly the dehydration processes. We hypothesize that elucidating the intricacies of these dehydration mechanisms is key to designing LIC materials with improved ionic conductivity. This study mainly focuses on the dehydration process of lithium indium chloride hydrate (Li₃InCl₆●xH₂O, LIC-xH₂O) via a water-mediated method to produce lithium indium chloride (Li₃InCl₆, LIC) under different conditions. Optimal ionic conductivity (3.2 × 10^-4 S cm^-1) was achieved under high vacuum and slow heating rates. In-situ characterization using synchrotron X-ray diffraction, X-ray absorption spectroscopy, and X-ray photoelectron spectroscopy revealed a two-step dehydration mechanism. The initial step of the dehydration process involves a solid-solution reaction, resulting in unit cell expansion and the release of H₂O. Rapid heating rates (>10°C min^-1) or inert atmospheres promote the formation of impurities, such as indium oxychloride (InOCl), which detrimentally affect ionic conductivity. Conversely, utilizing high-vacuum conditions and slow heating rates enables a controlled dehydration reaction, minimizing the formation of intermediate phases. This approach promotes the complete transformation of LIC-xH₂O into pure LIC, resulting in enhanced electrochemical performance for the material.