Synergic effect of CaI2 and LiI on ionic conductivity of solution-based synthesized Li7P3S11 solid electrolyte.

ABSTRACT

Li7P3S11 doped with CaX2 (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 CaX2 and LiI incorporated into the structure of Li7P3S11, while the remaining part existed at the grain boundary of the Li7P3S11 particle. The Raman peak positions of PS43- and P2S74- ions in samples 90Li7P3S11-5CaI2 and 90Li7P3S11-5CaI2-5LiI had shifted as compared to the Li7P3S11 sample, showing that CaI2 addition affected the vibration of PS43- and P2S74- ions. EDS results indicated that CaI2 and LiI were well dispersed in the prepared powder sample. The ionic conductivity at 25 °C of sample 90Li7P3S11-5CaI2-5LiI 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 CaI2 and LiI doping. This study encouraged the application of Li7P3S11 in all-solid-state Li-ion batteries.