Ionic conductivity enhancement in the (PEO)₉ LiCF₃SO₃ : ec Polymer electrolyte due to addition of nano Al₂O₃

Abstract

Polyethylene oxide (PEO)-based polymer electrolytes have been extensively studied in the recent past as they have emerged as potential candidates to be used as electrolyte membranes in solid-state electrochemical devices. One of the major disadvantages of these polymer electrolytes, however, is their low ionic conductivity at ambient temperatures. Ionic conductivity of PEO-based electrolytes at ambient temperatures has been enhanced either by adding ceramic fillers or plasticizers. However, up to now, no attempt has been made to study the combined effect of adding both the plasticizer as well as the inert filler.

Composite polymer electrolyte samples were prepared by solvent casting method by adding a mixture of 50 wt % ethylene carbonate (EC) and 10 wt % Al₂0₃ filler of pore size 5.8 nm to the (Composite polymer electrolyte samples were prepared by solvent casting method by adding a mixture of 50 wt % ethylene carbonate (EC) and 10 wt % Ah03 filler of pore size 5.8 nm to the (PE0)₉LiCF₃S0₃ electrolyte. Complex impedance measurements were carried out on disc-shaped samples sandwiched between two stainless steel electrodes each of 13 mm diameter, using a Schlumberger SI 1260 impedance analyzer in the 1 Hz to 10 MHz frequency range and in.the 25 ⁰C to 100·⁰C temperature range. Measurements were taken at 10 ⁰C intervals on heating. Maximum conductivity enhancement was obtained for the system (PE0)₉LiCF₃S0₃ + 50 wt% EC + 10 wt % Al₂0₃ compared to the other three systems:(a) (PE0)₉LiCF₃S0₃ (b) (PE0)₉LiCF₃S0₃+ 50 wt % EC and (c) ((PE0)₉LiCF₃S0₃ + 10 wt % Al₂0₃). The highest room-temperature-conductivity of the composite electrolyte was 8.06x 10⁻⁵ S cm⁻¹ . Thus, a conductivity enhancement of more than two orders of magnitude has been achieved for (PE0)₉LiCF₃S0₃ + 50 wt % EC + 10 wt % Al₂0₃) system. It is suggested that the conductivity enhancement occurs mainly by two mechanisms. The plasticizer (EC) would contribute by reducing degree of crystallinity by lowering the glass-transition-temperature of the polymer.Al₂0₃ filler would contribute to conductivity enhancement by producing additional sites for migrating ionic species through transient bonding with O/OH groups on the filler surface through Lewis acid- base type surface interactions.