FTIR and rheological studies of PMMA-based nano-dispersed gel polymer electrolytes incorporated with LiBF4 and SiO2

Gel polymer electrolytes (GPEs) were prepared by dissolving lithium tetrafluoroborate (LiBF4) salt, poly(methylmethacrylate) (PMMA) polymer and distinct non-volatile solvents propylene carbonate (PC), and -N,N-dimethylformamide (DMF) in single as well as binary solvent mixtures. Ionic conductivities of 8.93 mS/cm and 6.68 mS/cm at 25 °C have been obtained for gel polymer electrolytes for 10 wt% PMMA in the solution of LiBF4 in binary solvent mixture of PC:DMF in (1:1) and (2:1) volume ratios respectively. The dispersion of nano-sized silica in gel polymer electrolyte not only exhibits small change in ionic conductivity but also enhances the mechanical strength as well as viscosity of gel polymer electrolytes. At room temperature, the ionic conductivity has been found to be 8.00 mS/cm for 6 wt% nano-sized silica in GPEs. Fourier-transform infrared (FTIR) spectroscopic studies have been used to scrutinize the corroboration of the complexation between PMMA, LiBF4, PC, DMF, PC:DMF, and SiO2. The interactions between salt and solvents in liquid electrolytes have also been analyzed by FTIR spectroscopy illustrating the strong interaction between lithium salt and solvent molecules. The appearance/disappearance and shifting of some peaks confirm the interaction among the constituents of nano-dispersed gel polymer electrolytes. The mechanical strength was confirmed by dynamic mechanical analysis (DMA) and viscosity [ηPC:DMF (2:1) > ηPC:DMF (1:1) > ηPC] for nano-dispersed silica-based gel polymer electrolytes. The electrical and mechanical stability with high ionic conductivity for such gel polymer electrolytes makes these electrolytes suitable for many device applications like high energy density lithium-ion batteries, super-capacitors, electro-chromic devices etc.