Ionic conduction mechanisms in 70Li(2)S-30P(2)S(5) type electrolytes: experimental and atomic simulation studies

Abstract

Although understanding the structure-property relationship in solid electrolytes is pivotal to develop electrolytes with improved properties, previous studies examined only the partial effect of the structures and did not consider the realistic operating environments. Here, experimental investigations and theoretical simulations are used to explore the collective effects of crystal structure, temperature, and electric field on the ionic conductivity of various electrolytes with the 70Li(2)S-30P(2)S(5) composition. Each electrolyte sample is composed of a mixture of three distinct crystalline phases: gamma-Li3PS4, Li7P3S11, and Li4P2S6, each of which is comprised of the PS4, P2S7, and P2S6 substructures in varying fractions and spatial distributions. Atomic simulations confirm that the abundant stable Li interstitial sites in these crystals, particularly Li7P3S11, shorten the jumping distance for Li self-diffusion. On the other hand, charge polarization of the P2S7 cluster amplifies its oscillatory motion in the presence of an electric field and at ambient temperatures, thereby widening the Li diffusion passage. The reduction in the Li jumping distance, as well as the widening of the diffusion passage, reduce the energy barriers for Li diffusion, allowing for fast Li transport. While the present findings fill the knowledge gaps regarding the ionic conduction mechanisms of the 70Li(2)S-30P(2)S(5) electrolytes, they also provide design criteria for developing highly conductive solid electrolytes.(c) 2022 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.