Stretching Ion Conducting Polymer Electrolytes: In-Situ Correlation of Mechanical, Ionic Transport, and Optical Properties

Abstract

In this work we perform mechanical stretching tests while monitoring optical and ionic transport properties of ion-intercalated semi-crystalline polyethylene-oxide (PEO) electrolytes in-situ. Utilizing ionic liquid (EMIBF4) – PEO electrolytes, we demonstrate a correlation between the degree of crystallinity, which depends on the ion concentration, and the Young's modulus, ultimate tensile strength, and yield stress. Upon stretching solid-state PEO electrolytes, we observe an anisotropic increase in ionic conductivity that we correlate to the optical polarized Raman spectroscopic and microscopic signatures of polymer domain alignment - especially notable in the plastic regime. In-situ Raman spectroscopic studies indicate mechanically-induced ionic transport effects originate from chemical and structural rearrangement of polymer chains, and are independent of the ion species utilized. To emphasize this, we demonstrate the ideas of this study to be similarly transferrable to LiPF6 and LiI/I2 intercalated PEO solid-state electrolytes which exhibit similar mechanical-ionic transport response as ionic liquids. This study lays the groundwork for studying the mechanochemistry of solid-state electrolytes, with relevance toward specific electrolyte configurations employed in supercapacitors, lithium ion batteries, and dye sensitized solar cells.