Structure-conduction correlations in a chlorine-rich superionic lithium-argyrodite solid electrolyte: A DRT analysis

The argyrodite-type Li7−xPS6−xClx (LPSC) solid electrolyte is a promising candidate for Ah-scale all-solid-state Li-ion batteries due to its high ionic conductivity of over 10 mS cm−1. Understanding the influences of scalable synthesis conditions on the material structure and performance of LPSC is critical in industrial production. Herein, electrochemical impedance spectroscopy (EIS) combined with the distribution of relaxation times (DRT) analysis method was first applied to demonstrate the structure-conductivity relationships for the superionic Li+ conduction in LPSC to determine the optimum sintering temperature. The DRT tool enables the specific quantification of the ultrahigh lithium-ion kinetics in LPSC bulk/grain boundaries, which cannot be revealed by conventional fitting Nyquist plots. Detailed structural characterizations, such as X-ray diffraction (XRD) and scanning electron microscopy (SEM), were conducted to assist in analyzing the structural changes in the bulk and grain boundaries of LPSC. Finally, the Li5.4PS4.4Cl1.6 solid electrolyte sintered at 480 °C delivered the purest phase with the highest Li+ conductivity due to the lowest amount of grain boundaries and the shortest intercage ion leap distance in the unit cell. Thus, a narrow sintering temperature window is determined for obtaining LPSC with optimized performance. This work provides a novel DRT-assisted analysis protocol for exploring the craft-structure-performance correlations in LPSC, which helps guide industrial production.