Ionic conductivity, SEM, TGA and rheological studies of Nano-dispersed silica based polymer gel electrolytes containing LiBF4

Polymethylmethacrylate (PMMA) based nano-dispersed polymer gel electrolytes containing lithium tetra-fluoroborate (LiBF4), non-volatile solvents: propylene carbonate (PC) as single solvent, binary solvent mixtures with N,N-dimethylformamide (PC:DMF) in different volume ratios and nano-sized silica have been prepared and characterized. Ionic conductivity of gel as well as liquid electrolytes depends mainly upon the donor number and viscosity of the solvents used. Maximum ionic conductivity of 9.4 x 10(-3) S/cm at 25 degrees C has been obtained for nano-dispersed silica based polymer gel electrolyte having (PC:DMF = 1:1) volume ratio. Small content of PMMA in gel electrolyte improves the ionic conductivity, whereas small content of nano-sized silica not only enhances the ionic conductivity, but also improves the mechanical strength of the electrolyte. Two conductivity maxima observed at very low content of nano-sized silica in PMMA based gel electrolytes for binary solvent mixture having 2:1 and 1:1 volume ratios have been explained by double percolation threshold model. Moreover nano-dispersed silica based polymer gel electrolytes show good thermal properties, which have been confirmed by Differential Scanning Calorimetry (DSC) & Thermo Gravimetric Analysis (TGA) and mechanical properties have been studied by Dynamic Mechanical Analysis (DMA) studies. Also, the ionic conductivity of nano-dispersed silica based polymer gel electrolytes show typical curvature behavior as compared to polymer gel electrolyte over the temperature range of 10 degrees C-70 degrees C indicating their high amorphous nature. Also, the comparative results have been observed via activation energies for polymer gel electrolytes with and without silica, which have been calculated from logo vs. 1000/T plot. The behavior of the plot does not show much change at all temperature regions (change is only by a factor), which compile acute in distinct electrochemical devices.