Physico-Chemical, Thermal, and Electrochemical Analysis of Solid Polymer Electrolyte from Vegetable Oil-Based Polyurethane

In this paper, we report the preparation of bio-based polyurethane (PU) from renewable vegetable oil. The PU was synthesized through the reaction between jatropha oil-based polyol and isocyanate in a one-shot method. Then, lithium perchlorate (LiClO4) salt was added to the polyurethane system to form an electrolyte film via a solution casting technique. The solid polymer electrolyte was characterized through several techniques such as nuclear magnetic resonance (NMR), Fourier transforms infrared (FTIR), electrochemical studies, thermal studies by differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA). The NMR analysis confirmed that the polyurethane was successfully synthesized and the intermolecular reaction had occurred in the electrolytes system. The FTIR results show the shifting of the carbonyl group (C=O), ether and ester group (C–O–C), and amine functional groups (N–H) in PU–LiClO4 electrolytes compared to the blank polyurethane, which suggests that interaction occurred between the oxygen and nitrogen atom and the Li+ ion as they acted as electron donors in the electrolytes system. DSC analysis shows a decreasing trend in glass transition temperature, Tg and melting point, Tm of the polymer electrolyte as the salt content increases. Further, DMA analysis shows similar behavior in terms of Tg. The ionic conductivity increased with increasing salt content until the optimum value. The dielectric analysis reveals that the highest conducting electrolyte has the lowest relaxation time. The electrochemical behavior of the PU electrolytes is in line with the Tg result from the thermal analysis.