Ionic conduction mechanisms in 70Li₂S−30P₂S₅ type electrolytes: experimental and atomic simulation studies

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 70Li₂S−30P₂S₅ composition. Each electrolyte sample is composed of a mixture of three distinct crystalline phases: γ-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 70Li₂S−30P₂S₅ electrolytes, they also provide design criteria for developing highly conductive solid electrolytes.