Lithium Ion Conducting Glasses and Glass-Ceramics in the Systems Li₂S-M_xS_y (M=Al, Si and P) Prepared by Mechanical Milling

Abstract

Amorphous solid electrolytes in the system Li₂S-Al₂S₃ were prepared by a mechanical milling technique for the first time. The 60Li₂S•40AlS_1.5 (mol%) amorphous solid electrolyte showed the maximum conductivity of 3.4×10^-5 S cm^-1 at room temperature in tablet shape. The Li₂S-Al₂S₃ system proved to show lower conductivity than the Li₂S-SiS₂ and Li₂S-P₂S₅ systems in an amorphous state because the latter two systems exhibited the conductivities of 10^-4 S cm^-1 at room temperature. Glass-ceramics in the system Li₂S-Al₂S₃ were directly obtained by mechanical milling at a higher rotation speed, suggesting that glass-ceramic electrolytes as well as glassy ones were prepared by controlling the milling conditions. The crystal Li₅AlS₄ precipitated from the system Li₂S-Al₂S₃ lowered the conductivity. On the contrary, the conductivity enhancement by crystallization was observed for the 67Li₂S•33PS_2.5 (mol%) glass and the obtained glass-ceramic exhibited high ambient temperature conductivity of about 10^-3 S cm^-1. The crystallization of a superionic crystal analogous to the thio-LISICON Li_3.25Ge_0.25P_0.75S₄ was responsible for the marked conductivity enhancement.