Exploring dehydration mechanisms and conductivity optimization in Li3InCl6·xH2O via in situ synchrotron techniques

Abstract

In recent years, halide solid electrolytes have attracted considerable attention because of their high ionic conductivity and wide electrochemical window. These electrolytes can be prepared as pure phases through a water-based route. However, the mechanism of dehydration reactions in these electrolytes has not been considered thoroughly. This work investigates the dehydration process of lithium indium chloride hydrate (Li₃InCl₆·xH₂O; LIC–xH₂O) using a water-mediated method to form lithium indium chloride (Li₃InCl₆; LIC). The ionic conductivity measurements indicate that an optimal conductivity of 3.2 × 10⁻⁴ S cm⁻¹ is achieved at low heating rates and under high-vacuum conditions. In situ synchrotron X-ray diffraction, X-ray absorption spectroscopy, and X-ray photoelectron spectroscopy demonstrate that dehydration follows a two-step reaction. The first step involves a solid-solution response with unit cell expansion to remove H₂O. The results indicate that high heating rates (above 10 °C min⁻¹) or inert atmospheric conditions lead to the formation of impurities, such as indium oxychloride (InOCl), which hinder ionic conductivity. In contrast, utilizing high-vacuum conditions combined with a slow heating rate enables an optimal dehydration reaction. This approach facilitates the elimination of intermediate phases, which subsequently transform into pure LIC through the progression of the reaction.