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.