Impact of hydration on ion transport in Li2Sn2S5·xH2O

Abstract

This work investigates the structure and transport properties of the layered material Li2Sn2S5·xH2O. The anhydrous phase shows a room-temperature Li+diffusivity below 10−9cm2s−1and conductivity below 10−5S cm−1. Upon exposure to humidity, water intercalates between the layers and increases the interlayer distance, inducing first-order transitions to a hydrated phase (x≈ 2-4) and then to a second hydrated phase (x≈ 8-10). The latter is soft and sticky but remains solid. Diffusion of both Li+ions and H2O remains predominantly two-dimensional under all conditions. The Li+diffusivity and conductivity both increase by three orders of magnitude upon hydration, reaching values of 5 × 10−7cm2s−1and 10−2S cm−1in the second hydrate. These transport rates are extraordinary for a solid electrolyte and approach what is typically seen in aqueous solutions. The material Li2Sn2S5·xH2O thus bridges the gap between a hydrated solid electrolyte and a confined liquid electrolyte, which is scientifically interesting and potentially useful in battery applications. In the light of these findings, a previous work on Li2Sn2S5from our groups is revisited.