Effect of surface modification of dispersoid on hybrid polymer electrolyte

This study reports the properties of hybrid polymer electrolyte films obtained via incorporating varying amounts of surface modified SiO2 nanoparticles and electrolyte solution (1 M LiBF4 in EMIMBF4) in PVdF-HFP. The SiO2 nanoparticles (diameter ~100–150 nm) have been synthesized by the conventional Stober's method and further modified chemically in two steps, viz., (i) carboxylation and (ii) EDC-NHS coupling. The surface modification of the nanoparticles has been confirmed by FTIR and XRD. The effect of addition of modified SiO2 and/or electrolyte solution has been studied using different characterization techniques. The positive impact of surface modification is evident by the reduced aggregation of the surface modified nanoparticles in the host matrix as compared to the unmodified ones (SEM micrographs). The effect of better dispersion of the modified nanoparticles in the polymer matrix has been reflected by the enhanced ionic conductivity (at room temperature) of modified SiO2 added electrolyte film (~2.94 mS/cm) compared to the films with no SiO2 and unmodified SiO2 (~1.90 mS/cm and ~1.56 mS/cm, respectively). The hybrid electrolyte film with maximum ionic conductivity has exhibited a wide electrochemical stability window (~5.5 V) and good mechanical and thermal stability (up to ~300 °C). The optimized hybrid film has been further used to fabricate an electric double layer capacitor (EDLC). The electrochemical performance of the cell has been studied using electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) techniques.