Impact of Short Chain Polymer in Ionic Conductivity for Polymer Solid-State Electrolyte Towards Inter-/Intramolecular O-H Bond

Abstract

Poly(ethylene oxide) (PEO) was first developed as a conducting polymer over a half-century ago and is still the most fascinating electrolyte matrix to use in solid-state batteries. Although thousands of articles have been published on the conductivity of various PEO-based solid-state electrolytes, none of the studies involved a higher EO-to-salt ratio up to 85 to 1. In this study, solid polymer electrolytes (SPE) based on the PEO-PEG complex with Sodium(I) Bis(trifluoromethanesulfonyl)imide (NATFSI) were prepared using the solid-state synthesis methods. The measurement using the Electrochemical Impedance Spectroscopy (EIS) technique demonstrated that EO70Na - 9PEO:3PEG has the most optimum PEO-PEG-NATFSI electrolyte system with conductivities of 0.01 mS/cm and 0.13 mS/cm at 25 °C and 50 °C, respectively. As reported in published articles, the conductivity of the EO to Na ratio started to decline from 15:1 to 25:1 with the dropped in NATFSI concentration. Further decline of Na concentration with the addition of EO from 40 to 70 ratio indicates a new increasing trend for the conductivity series, which result in a bimodal graph distribution. Fourier transform infrared (FTIR) spectral studies for PEO-PEG-based SPE revealed that vibrational changes of intramolecular -OH change as the concentration of short-chain polymer backbone and salt varies. The Raman spectral studies for PEO-PEG-based SPE proposed that the percentage of bis(trifluoromethane)sulfonimide anion (TFSI- anions) increases with the increase in ratio from 15 to 70 of EO to Na. It is proposed that a higher percentage of both intramolecular -OH and TFSI- anions are crucial in providing high conductivity value. The structure of complexed PEO-PEG-based SPE from XRD suggested that the crystalline domain of SPE decreased with the smaller amount of NATFSI.