Ionic liquid-based sodium ion-conducting composite gel polymer electrolytes: effect of active and passive fillers.

We report the studies on composite gel polymer electrolytes (GPEs) comprising 0.5 M solution of sodium trifluoromethane sulfonate (Na-triflate or NaTf) in ionic liquid 1-ethyl 3-methyl imidazolium trifluoromethane sulfonate (EMITf) entrapped in poly (vinylidinefluoride-co-hexafluoropropylene) (PVdF-HFP) dispersed with passive filler AlO and active filler NaAlO particles. The free-standing films of the composite GPEs, prepared from solution-cast method, offer optimum ionic conductivity at room temperature (6.3-6.8 × 10 S cm and 5.5-6.5 × 10 S cm for AlO- and NaAlO-dispersed GPEs, respectively), with sufficient electrochemical stability and excellent thermal stability up to 340 °C. As observed from XRD and SEM, the composites are of predominantly amorphous and porous character, which support the high ionic conduction. The sodium ion transport number has been found to be ∼0.27 for AlO-dispersed GPE and 0.42 for NaAlO-dispersed GPE, which indicates the predominant role of passive and active fillers, AlO and NaAlO, respectively. The dispersion of NaAlO enhances the sodium ion conductivity in composite GPE substantially. The overall ionic conductivity is same as in the case of AlO dispersion. The performance characteristics of GPE, particularly, dispersed with active filler NaAlO show its potential applicability as electrolyte/separator in sodium batteries. [ABSTRACT FROM AUTHOR]