Mechanical deformation effects on ion conduction in stretchable polymer electrolytes

Abstract

Flexible and stretchable energy storage devices, including batteries, supercapacitors, and ionic piezoelectrics, have garnered substantial research interest in recent years to address a wide range of applications such as smart textiles and medical implants. These devices are intended to undergo mechanical deformation, and the impact of deformation on electrochemical performance is not well understood. One important area of focus is studying how mechanical deformation influences ion conduction in polymer electrolytes. In this work, a dual theoretical and experimental approach is taken to further evaluate this phenomenon. A stretchable solid polymer electrolyte film subjected to tensile deformation (approximately 48% strain), through which ion diffusion occurs, is analyzed using a continuum approach treating ion diffusion and mechanical deformation as coupled. Thermodynamic laws are applied to obtain governing multiphysics equations accounting for large deformation mechanics and material nonlinearity. The theoretical solution obtained demonstrates how through-plane ionic conductivity changes when the polymer is subjected to stretching. Evolutionary materials deformation of the polymer electrolyte is considered to elucidate the underlying driving physical mechanisms of ion conduction. An experiment was also conducted to measure change in through-plane ionic conductivity with applied uniaxial strain in a sample of polyethylene oxide (PEO), a material commonly used as the electrolyte in solid polymer electrolyte lithium ion batteries. The experimental results show a greater than 1600% ionic conductivity enhancement for approximately 48% strain. The theoretical and experimental results are in good agreement and show that ion conduction is enhanced with increasing strain following an exponential function for a PEO electrolyte.