Influence of precipitate/supernatant ratio during liquid-phase synthesis of solid electrolyte Li7P3S11

Delicate control of the precipitate/supernatant ratio in the precursor suspension during liquid-phase synthesis of Li7P3S11 provides information on how the morphology of the impurities affects the ionic conductivity. In this work, the influence of the precipitate/supernatant ratio on the phase structure, the morphology and the ionic conductivity of Li7P3S11 prepared in acetonitrile is studied. It is revealed that in the supernatant-excess region, the excess amorphous “Li2S·P2S5” finally turns into a poorly ionic conductive phase Li4P2S6 which wraps Li7P3S11 particles, increasing the interfacial resistance. In the precipitate-excess region, a thio-LISICON III phase turned from the excess precipitate tends to stay within Li7P3S11 particles, and therefore its negative influence on the total ionic conductivity is not evident. Consequently, a slight composition shift into the precipitate-excess region benefits the ionic conductivity of the resultant solid electrolyte. [Display omitted] •Precipitate/supernatant ratio was adjusted during liquid-phase synthesis of Li7P3S11.•Excess precipitate inhibits the formation of paste-like poor-conductive Li4P2S6.•The highest ionic conductivity was achieved when the precipitate was slightly excess.