Synergic effect of CaI 2 and LiI on ionic conductivity of solution-based synthesized Li 7 P 3 S 11 solid electrolyte.

Li 7 P 3 S 11 doped with CaX 2 (X = Cl, Br, I) and LiI solid electrolytes were successfully prepared by liquid-phase synthesis using acetonitrile as the reaction medium. Their structure was investigated using XRD, Raman spectroscopy and SEM-EDS. The data obtained from complex impedance spectroscopy was analyzed to study the ionic conductivity and relaxation dynamics in the prepared samples. The XRD results suggested that a part of CaX 2 and LiI incorporated into the structure of Li 7 P 3 S 11 , while the remaining part existed at the grain boundary of the Li 7 P 3 S 11 particle. The Raman peak positions of PS 4 3- and P 2 S 7 4- ions in samples 90Li 7 P 3 S 11 -5CaI 2 and 90Li 7 P 3 S 11 -5CaI 2 -5LiI had shifted as compared to the Li 7 P 3 S 11 sample, showing that CaI 2 addition affected the vibration of PS 4 3- and P 2 S 7 4- ions. EDS results indicated that CaI 2 and LiI were well dispersed in the prepared powder sample. The ionic conductivity at 25 °C of sample 90Li 7 P 3 S 11 -5CaI 2 -5LiI reached a very high value of 3.1 mS cm -1 due to the improvement of Li-ion movement at the grain boundary and structural improvement upon CaI 2 and LiI doping. This study encouraged the application of Li 7 P 3 S 11 in all-solid-state Li-ion batteries.