Understanding interfacial stability and ionic transport in ethanol-synthesized Li3InCl6 solid electrolyte for all-solid-state batteries

The development of safe, high-energy-density all-solid-state batteries (ASSBs) hinges on solid electrolytes that combine high ionic conductivity with chemical and electrochemical stability. In this work, we investigate the physico-chemical and interfacial properties of Li 3 InCl 6 synthesized via an ethanol-mediated route, offering a scalable, low-energy alternative to conventional processing methods. The resulting material exhibits high phase purity and relatively high room-temperature ionic conductivity (0.73 mS·cm -1 ), being readily densifiable under cold pressing and maintaining structural integrity. Interfacial reactivity with lithium and indium metal anodes was systematically studied using electrochemical impedance spectroscopy (EIS), distribution of relaxation times (DRT) analysis, and X-ray diffraction (XRD). While lithium induces rapid formation of a resistive solid electrolyte interphase (SEI), indium significantly mitigates interface degradation by forming a Li-In alloy that enhances chemical stability and cycling performance. Symmetric stripping/plating tests demonstrate stable long-term cycling under pressure and elevated temperature in cells employing Li-In composite anodes. This work highlights the importance of interfacial engineering for halide-based solid electrolytes and introduces DRT as a valuable analysis tool to resolve and monitor dynamic degradation processes at buried interfaces in ASSBs. • Interfacial analyses confirm the known reactivity of Li 3 InCl 6 with lithium metal • The use of Li alloys is the most promising interfacial strategy to improve the generally poor SEI stability of this class of materials. • This study provides a time-resolved, process-deconvoluted analysis of SEI formation and charge-transfer resistance via distribution of relaxation times (DRT) analysis, enabling a more nuanced understanding of buried interface behavior.