Sulfide solid electrolytes in the Li2S–P2S5 system were synthesized by a liquid phase process under ultrasonic irradiation, and heat treatments at low temperatures. Crystal phase, structure, morphology and ionic conductivity… Click to show full abstract
Sulfide solid electrolytes in the Li2S–P2S5 system were synthesized by a liquid phase process under ultrasonic irradiation, and heat treatments at low temperatures. Crystal phase, structure, morphology and ionic conductivity of the sulfide electrolytes were examined after solvent removal at 180 °C and two different heat treatment temperatures, 220 °C and 250 °C. The study revealed that the ionic conductivities of the xLi2S·(100 − x)P2S5 sulfide electrolytes, in compositions with 70 ≤ x ≤ 75 mol%, are largely influenced by the local structure. The heat treatment at 220 °C was found to be an adequate temperature to promote crystallization of the high ionic conductive Li7P3S11 phase. Higher temperatures for heat treatment such as 250 °C lead to the formation of P2S64− (hypo-thiodiphosphate) units in the local structure of the sulfide electrolytes leading to a reduction of ionic conductivity. The formation and distribution of PS43− (ortho-thiophosphate), P2S74− (pyro-thiophosphate) and P2S64− units in the local structure were found to be key factors in achieving higher ionic conductivity (up to 10−3–10−4 S cm−1 at room temperature).
               
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