Ionic conductivity of solid polymer electrolytes depending on elongation

Abstract

Research on solid polymer electrolytes (SPEs) based on poly(ethylene oxide) (PEO) is essential to propose an alternative to the conventional liquid electrolyte in order to increase both the mechanical properties and the ionic conductivity. Strategies to increase the ionic conductivity of SPEs are typically based on the development of new polymer architectures, lithium salt natures, plasticizers, or additives. In addition, applying an external field such as magnetic, electric, pressure, or a mechanical deformation onto the SPEs can alter the resulting ionic transport properties. For the later one, the main difficulty lies in obtaining the instantaneous evolution of the ionic conductivity coupled with the mechanical deformation and its geometrical change, especially when a striction domain appears. For this, a dedicated sample environment was designed to perform tensile tests in an inert atmosphere on SPE membranes at different temperatures (below and above the PEO melting temperature). Moreover, a methodology to calculate the instantaneous in-plane ionic conductivity is proposed based on COMSOL simulations to back out the sample geometrical changes during elongation. A strong impact on the in-plane ionic conductivity is observed when comparing PEO electrolyte architectures; from homopolymer to crosslinked single-ion conducting via binary conducting block copolymer electrolytes. Below the PEO melting temperature, a striction domain appears upon elongation whose conductivity is higher than the one of the bulk by a factor 1.7 and 18 for PEO homopolymer and binary conducting PEO-based block copolymer electrolytes, respectively.