The effects of $α-Al_2O_3$ content and temperature on the ionic conduction characteristics of the polycrystalline lithium iodide containing 0 to 40 mol% α-alumina were studied at various temperature from 25±3℃ to 100±5℃ by using AC impedance techniques. Also, the effect of DC potential on the AC impedance behavior of LiI/$α-Al_2O_3$ was investigated at room temperature. The ionic conductivity of LiI/$α-Al_2O_3$ solid electrolyte increased with increasing $α-Al_2O_3$ content. The activation energy for ionic conduction remained almost constant regardless of $α-Al_2O_3$ content, and was found to be about 50 kJ/mol. X-ray diffraction pattern revealed that second phase was not formed in LiI/$α-Al_2O_3$ solid electrolyte during the specimen preparation. The AC resistance of the LiI/$α-Al_2O_3$ measured at 5 Hz increased with increasing DC potential up to 1000 mV, and then decreased up to 1500 mV, followed by abruptly decreasing at 1500mV. From these results, ionic conduction mechanisms of LiI/α-Al_2O_3$ are discussed in terms of space charge layer model and the second phase model. It is suggested that ionic conductivity enhanced by $α-Al_2O_3$ doping was caused by increasing space charge layer.
