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Recently, several sulfide solid electrolytes have been synthesized by liquid-phase synthesis for the commercialization of all-solid-state batteries. Unfortunately, the ionic conductivity for most of these electrolytes is unsatisfactory compared to that of solid electrolytes synthesized by conventional ball milling. This problem is attributed to different mechanisms between the liquid phase and the solid phase in reaction and formation. However, to the best of our knowledge, the effect of the solvent on the ionic conductivity of solid electrolytes has not been extensively investigated, although the identification of these properties is a key point in understanding the liquid-phase synthesis. Herein, the correlation between ionic conductivity and crystallinity originating from the solvents used has been investigated. As a result, the ionic conductivity of the electrolyte was found to be strongly dependent on polarity (δP) with low crystallinity. The highest ionic conductivity (5.09 × 10–4 S cm–1 at 25 °C) was obtained using butyl acetate, which exhibited the lowest δP. Moreover, the highest ionic conductivity of Li3PS4 produced by liquid-phase synthesis using butyl acetate was very comparable to that obtained by ball milling (5.14 × 10–4 S cm–1).
Yamamoto et al. (Fri,) studied this question.