Abstract: In the past years, lithium-ion solid-state batteries demonstrated significant advancements regarding such properties as safety, long-term endurance, and energy density. The properties of these depend on solid-state electrolytes and especially ionic transport interfacial transport with cathode or anode materials. Solid-state electrolytes based on lithium halides offer new opportunities due to their unique features such as broad electrochemical stability window, high lithium-ion conductivity, and elasticity at close to melting point temperatures that help to improve lithium-ion transport at interfaces. A comparative study of lithium indium halide (Li3InCl6) electrolytes syn-thesized by a mechano-thermal method using different optimization parameters revealed a signif-icant effect of ball-milling time, temperature, and pressure on lithium-ion transport. Based on the Electrochemical Impedance Spectroscopy (EIS) data in the temperature range of 25-100 °C, the optimized Li3InCl6 electrolyte phase demonstrates high ionic conductivity reaching 0.98 mS cm−1 at room temperature. However, at 70 °C, phase transformation was observed leading to significant changes in the activation energy for lithium-ion transport. In-situ X-ray diffraction and in-situ/operando X-ray photoelectron spectroscopy techniques confirmed the tempera-ture-dependent behavior of Li3InCl6 synthesized. These observations provide critical information for practical applications of solid-state electrolytes and nanocomposites based on Li3InCl6 within the broad temperature range for lithium-ion solid-state batteries with improved morphology, chemical interactions, and structural integrity.