FTIR studies on interactions among components in PVdF-HFP:PC:MPII electrolytes

Abstract

Liquid electrolytes are known to have high conductivities. However, they suffer from leakage, corrosion of electrodes and other stability issues. Solid polymer electrolytes eliminate the problems of liquid electrolytes at the cost of lower conductivity. Quasi-solid-state polymer electrolytes (QSSPE) overcome the shortcomings of both liquid electrolytes and solid polymer electrolytes. In this work, QSSPE is prepared by incorporating poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP) in a propylene carbonate (PC) and 1-methyl-3-propyl imidazolium iodide (MPII) liquid electrolyte. Fourier transform infrared (FTIR) studies have been carried out to investigate the interactions among PVdF-HFP, PC and MPII. A comprehensive spectroscopic investigation on ion-solvent-polymer interactions helps to understand the mechanism of ionic conduction in the PVdF-HFP/PC/MPII electrolyte system. Interaction between MPII and PC has occurred from the changes in the ν(C=O), ν(C-O) + ω(C-H), ω(C-H) + δ(C-H) and τ of ring of PC as well as the C-N bond oscillation and of (N-C-H) of MPII. Interaction occurs via the coordination of MPIm+ cations with both oxygen atoms of PC. Complexation between PVdF-HFP and MPII has been noted. MPII suppresses the non-polar α-phase and induces the polar β and -phases of PVdF-HFP. Shift of peaks belong to the CF2 and CF3 groups of PVdF-HFP suggests the complexation occurs at the fluorine atoms in CF2 and CF3 groups. Evidence of interaction between PC and PVdF-HFP has been manifested through the change of the ν(C=O), τ(C-H) + δ(C-H) and ν of the CF2 group of PVdF-HFP. Disappearance of non-polar α-phase of PVdF-HFP is noted in the presence of PC. From this work, the authors hope to shed some light on understanding the conduction mechanism in PVdF-HFP:PC:MPII electrolytes. Understanding the conduction mechanism is important in order to find ways for conductivity improvement.