Unveiling the Chemical Stability and Solvent Compatibility of Halide Solid-State Electrolytes: Insights from Isothermal Calorimetric Titration and Synchrotron Spectroscopy

As interest in next-generation all-solid-state batteries (ASSBs) grows, understanding the impact of solution-based processing on solid-state electrolytes (SSEs) becomes crucial. This study examines the interaction of Li3InCl6 (LIC), a halide SSE, with various solvents, including protic, aprotic polar, and nonpolar types. LIC powder is mixed with ten solvents selected for their diverse physical and chemical properties. Through a series of analytical techniques, this study explores the compatibility of LIC with different solvent environments. The LIC–solvent mixtures are analyzed through color observation, pH measurement, and isothermal calorimetric titration. Moreover, after solvent removal, the dried LIC powder is further characterized using diffraction and various advanced spectroscopic techniques. The findings reveal that LIC is chemically stable in nonpolar solvents but exhibits instability in most polar solvents, with ethanol showing the highest stability among the polar options. It is also observed that indium reacts with highly electronegative elements such as oxygen and nitrogen based on the hard–soft acid–base principle. Furthermore, LIC in protic solvents results in acidic solutions, whereas in aprotic solvents, it exhibits basicity. These results are crucial for the development of ASSBs and underscore the importance of understanding the chemical compatibility of LIC with various solvent systems for advanced energy storage applications.