Urea-assisted ion-transport behavior in magnesium ion conducting solid polymer electrolyte membranes intended for magnesium batteries

Abstract

In this paper, performance enhancement of magnesium ion conducting solid polymer electrolyte has been investigated with the incorporation of urea in it. The standard solution casting technique has been adopted to fabricate solid polymer electrolyte consisting of poly(ethylene oxide) (PEO) polymer, magnesium triflate (MgTf 2 ) salt and urea. Measurement on conductivity, dielectric and modulus is carried out on the electrolyte films as a function of frequency at various temperatures. On the introduction of urea in PEO/MgTf 2 matrix, the ionic conductivity improves by an order of magnitude and the relaxation time decreases from 0.45 to 0.16 µs. The highest conductivity of 6.3 × 10 -5 S cm −1 has been recorded for PEO/MgTf 2 /Urea polymer electrolyte system. The ionic conductivity versus temperature plots suggests the Arrhenius behavior within the electrolyte compositions. The number density of the free ions increases by an order of magnitude from 10 20 to 10 21 on the addition of urea in PEO/MgTf 2 matrix without any significant change in mobility values. The conductivity, dielectrics, surface morphology and X-ray diffraction studies reveal that urea is not only improving the porous structure but also interacting with the PEO/MgTf 2 matrix to improve the ion dynamics. This approach toward improved ion-transport behavior may be utilized in fabricating high-performance electrolytes, especially for magnesium batteries.