Ionic Conductivity and Dielectric Properties of LiBF4 Doped PMMA/ENR 50 Filled Acid Modified SiO2 Electrolytes

Incorporation of silicon dioxide (SiO2) filler was proven to improve phase separation and ionic conductivity of polymethyl methacrylate/50% epoxidized natural rubber (PMMA/ENR 50) electrolytes. Unfortunately, SiO2 was found agglomerated in PMMA/ENR 50 electrolytes thus restricting surface contact between polymer electrolytes and electrodes. Therefore, in this study, SiO2 was chemically modified using hydrochloric acid (HCl) in order to improve dispersion of SiO2 in PMMA/ENR 50 electrolytes matrix. SiO2 was reacted with HCl in different acid concentrations for an hour at ambient temperature then dried in an oven for 24 hours at 120oC. The acid modified SiO2 (HCl-SiO2) was then blended with PMMA/ENR 50-tetrahydrofuran (THF) solutions and doped with lithium tetrafluoroborate (LiBF4). Polymer electrolytes were obtained by solvent casting in a Teflon dish under nitrogen gas flow then further dried in an oven. The ionic conductivity of PMMA/ENR 50 filled HCl-SiO2 electrolytes was analyzed using electrochemical impedance spectroscopy (EIS). Activation energy (Ea) was calculated from log ionic conductivity (log σ) versus 1000/T plot using Arrhenius equation. It was found that the ionic conductivity (σ) was slightly decreased due to the acid modification SiO2. However, further increase in HCl concentration lead to steady increase in the σ. The activation energy (Ea) was found inversely proportion to the σ. Dielectric constant (ɛʹ) and dielectric loss and (ɛʺ) were found to initially decrease upon the acid modification SiO2. However, the ɛʹ and ɛʺ observed increases as HCl concentration increased. Real part modulus (Mʹ) was lower at lower frequency but increases as frequency increased. The Mʹ peaks were observed at higher frequency. The peaks shifted to higher frequency as concentration HCl increased but still at lower frequency compared to polymer electrolytes filled with unmodified SiO2. Nevertheless, no peak was recorded in imaginary part Modulus (Mʺ).