A systematic study on structure, ionic conductivity, and air-stability of xLi4SnS4·(1−x)Li3PS4 solid electrolytes

In order to use sulfide all-solid-state batteries as power sources of electric devices, sulfide solid electrolytes with high ionic conductivity and high air-stability must be developed. Li3PS4 electrolytes have been used in all-solid-state batteries because of their relatively high ionic conductivity (4 × 10 −4 S cm−1 at 25 °C) and higher air-stability than those of other Li2S–P2S5 type solid electrolytes. Herein, the Li4SnS4–Li3PS4 system was investigated to (1) increase the ionic conductivity of Li3PS4 using excess Li carriers and (2) improve the air-stability of Li3PS4 by introducing air-stable Sn–S bonds. The structure, ionic conductivity, and air-stability of xLi4SnS4·(1−x)Li3PS4 were systematically investigated; the results showed that adding small amounts of Li4SnS4 to Li3PS4 glass and glass-ceramic enhanced their ionic conductivity and air-stability without degrading their electrochemical stability. In particular, the 0.3Li4SnS4·0.7Li3PS4 glass-ceramic showed an ionic conductivity of 8.1 × 10 −4 S cm−1 at 25 °C and generated only a small amount of H2S gas (3 ppm [0.3 cm3 g−1]) when it was dissolved in water. Hence, xLi4SnS4·(1−x)Li3PS4 solid electrolytes can be used as alternatives to the conventional Li3PS4 electrolyte because of their various advantages and a simple preparation method that involves adding only SnS2 to conventional starting materials.