Li4PS4I: A Li+ Superionic Conductor Synthesized by a Solvent-Based Soft Chemistry Approach

A novel crystalline lithium superionic conductor, Li4PS4I, has been discovered utilizing a solvent-based synthesis approach. It was found that the starting material Li3PS4·DME reacts with LiI in a 1:1 ratio in DME to give a precursor that results in Li4PS4I after soft heat treatment at around 200 °C in vacuum. Its crystal structure was solved ab initio by evaluating both X-ray (Mo-Kα1) and neutron (TOF, GEM, ISIS) powder diffraction data, in a combined refinement (P4/nmm, Z = 2, a = 8.48284(12) A, c = 5.93013(11) A, wRp = 0.02973, GoF = 1.21499). The final structure model comprises, besides Li+ ions, isolated PS43– tetrahedra in a layer-like arrangement perpendicular to the c-axis that are held apart by I– ions. The Li+ ions are distributed over five partially occupied sites residing in 4-, 5-, and 6-fold coordination environments. A topostructural analysis of the voids and channels within the PS4I4– substructure suggested a three-dimensional migration pathway system for the Li+ ions in Li4PS4I. The Li+ i...