Design and synthesis of room temperature stable Li-argyrodite superionic conductors via cation doping

Abstract

All-solid-state batteries receive tremendous attention owing to their potential in improving battery safety and electrochemical properties. Developing a suitable solid electrolyte (SE) is a significant factor for all-solid-state batteries. Herein, we report calculation prediction and experimental evaluation of a series of Li-argyrodites, Li_7+xM_xP_1−xS₆ (M = Si, Ge). The density functional theory method predicts the structural stability of argyrodite-type Li_7+xM_xP_1−xS₆ (M = Si, Ge), meanwhile, the argyrodite-type Li_7+xM_xP_1−xS₆ (M = Si, Ge) are successfully synthesized by a solid state reaction method. Using structure refinements of X-ray diffraction data and Raman spectroscopy, we discover that Si and Ge substitute the P in the 4b site. Si and Ge aliovalent doping in the original composition, Li₇PS_6, can make the desired cubic high-temperature (HT) phase of Li-argyrodites stabilized at room temperature and improve the ionic conductivities over 10⁻³ S cm⁻¹ which is 3 orders of magnitude higher than that of original Li₇PS₆. Moreover, the argyrodite-type Li_7+xM_xP_1−xS₆ (M = Si, Ge) show a wide electrochemical window and stability with lithium metal. Stabilized Li-argyrodites could be suitable solid electrolytes for application in all-solid-state batteries. This work also demonstrates that stabilizing the high-temperature phase with high ionic conductivity would be a promising approach to explore new ionic conductors.