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 70Li ₂S−30P ₂S ₅ composition. Each electrolyte sample is composed of a mixture of three distinct crystalline phases: γ-Li ₃PS ₄, Li ₇P ₃S ₁₁, and Li ₄P ₂S ₆, each of which is comprised of the PS ₄, P ₂S ₇, and P ₂S ₆ substructures in varying fractions and spatial distributions. Atomic simulations confirm that the abundant stable Li interstitial sites in these crystals, particularly Li ₇P ₃S ₁₁, shorten the jumping distance for Li self-diffusion. On the other hand, charge polarization of the P ₂S ₇ 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 ₂S−30P ₂S ₅ electrolytes, they also provide design criteria for developing highly conductive solid electrolytes.