Synthesis and Li + ion migration studies of Li 6PS 5X (X = Cl, Br, I)

Abstract

Lithium ion conducting argyrodite-type Li 6PS 5X (X = Cl, Br, I) compounds were prepared using mechanical milling followed by annealing. XRD characterization reveals the formation and growth of Li 6PS 5X crystals in samples under varying annealing conditions. Temperature dependent XRD data showed the monotonic increase of lattice constant within the range of study. For Li 6PS 5Cl and Li 6PS 5Br an ionic conductivity of the order of 10 -3 S/cm is reached at room temperature, which is close to the Li mobility in conventional liquid electrolytes and well suitable for all-solid-state safe electrochemical energy storage devices. Bond valence analysis of Li ion migration paths for the argyrodites showed the formation of low energy pathway cages around halide ion for Li 6PS 5Cl, around the sulfide ion for Li 6PS 5I. For higher activation energies these cages are interconnected to form a 3-D pathway network. In the case of Li 6PS 5Br cages around Cl and Br require about the same activation energy. © 2011 Materials Research Society.