Abstract

In this study, CaI₂-doped Li₄SnS₄ glass-ceramic solid electrolytes were prepared by heat treatment of glassy samples which were obtained by planetary ball- milling method. Thermogravimetric analysis – differential thermal analysis was used to determine the glass-ceramic transition temperature. The results showed that the CaI₂-doped solid electrolyte Li₄SnS₄ transformed from an amorphous structure to a hexagonal and orthorhombic phases at 240 and 368 ℃, respectively. The crystal structure of the glass-ceramic samples was determined by X-ray diffraction combined with Rietveld refinement. The ionic conductivity of the experimental samples (100-x)Li₄SnS₄-xCaI₂ (x = 0, 2, 5, 7, 10 and 15) after heat treatment at 390ºC for 1h in dry Argon atmosphere was measured by alternating current electrochemical impedance spectroscopy. Sample x = 7 had the highest ionic conductivity at 25ºC among the prepared samples and reached a value of 2.97×10^-4 Scm^-1. The ionic conductivity of orthorhombic Li₄SnS₄ is increased by CaI₂ doping because the formation of holes increases the number of ions that successfully make the jump to neighbor site. Notably, the activation energy E_a includes two components: E_f (activation energy for ion formation) and E_m (activation energy for ion movement). The E_m value decreases to a minimum at x = 7 and then increases again, indicating that the CaI₂ doping promotes the movement of Li⁺ ions.