Effect of Si substitution on the structural and transport properties of superionic Li-argyrodites

Abstract

Inspired by the recent interest in lithium ion conducting argyrodites as solid electrolytes for solid-state batteries, we have investigated the influence of aliovalent substitution in Li₆PS₅Br. Using Rietveld refinements against X-ray and neutron diffraction, coupled with impedance spectroscopy, we monitor the influence of Si⁴⁺ substitution for P⁵⁺ in Li_6+xP_1−xSi_xS₅Br on the structure and ionic transport properties. A step-wise incorporation of Si⁴⁺ leads to an expansion of the unit cell, as well as the inclusion of additional Li⁺ within the structure. The increasing Li content occupies the structural transition state and, in combination with the structural changes, leads to a three-fold improvement of the ionic conductivity. This work demonstrates that the argyrodite material class can be optimized through aliovalent substitution, thereby making argyrodites an ideal system for studying solid electrolytes within the field of solid-state batteries.