Electrical and electrochemical properties of magnesium ion conducting composite gel polymer electrolytes

The effect of micro- and nano-sized MgO and nano-sized SiO2 dispersion on the electrical and electrochemical properties of poly(vinylidene fluoride-hexafluoropropylene) (PVdF-HFP) based Mg2+ ion conducting gel polymer electrolyte has been investigated. The gel electrolytes have been characterized using electrical conductivity, cationic transport number (t+) measurements and cyclic voltammetry. A two-maxima feature has been observed in the 'conductivity versus composition' curve at ~3 wt% and 10–15 wt% of the filler contents. The highest conductivity has been obtained for the SiO2 dispersed gel electrolyte of ~1 × 10−2 S cm−1 for 3 wt% and ~9 × 10−3 S cm−1 at 15 wt% content. The value of 't+' is found to be enhanced substantially with increasing amount of MgO (both micro- and nanoparticles), whereas in the case of SiO2 dispersion the value does not increase substantially. The highest 't+' value of ~0.44 has been obtained for the addition of 10 wt% MgO nanoparticles. The enhancement in 't+' is explained on the basis of the formation of space-charge regions due to the presence of MgO : Mg2+-like species, which supports Mg2+ ion motion. A substantial increase in the amount of anodic and cathodic peak currents is observed due to the addition of nano-sized MgO particles in the gel polymer electrolyte, whereas in the cases of micrometre-sized MgO and nano-sized SiO2 the enhancement is not significant. The enhancement in conductivity in SiO2 dispersed nanocomposite gel electrolyte is predominantly due to anionic motion.