In the present work, effects of 100 MeV Si9+ ion irradiation of different fluences on poly(vinylidene fluoride-co-hexalluoro propylene) (PWIF-HFP)-layered silicate nanocomposite electrolyte membranes based on ionic liquid, 1-butyl-3-methylimidazolium bromide have been investigated. With increasing ion fluence, intercalation of PVdF-HFP into the interlayers of layered silicate increases eventually leading to exfoliation of silicate layers at the fluence of 5 x 10(11) ions cm(-2). Swift heavy ion (SRI) irradiation induces chain scissions in the polymer leading to increase in amorphicity due to which room temperature ionic conductivity increases with increasing ion fluence. Highest room temperature ionic conductivity of 4.96 x 10(-2) S cm(-1) has been obtained at the highest fluence of 1 x 10(12) ions cm(-2) employed in the present work. SRI irradiation increases the porosity of the nanocomposite electrolyte membranes as confirmed from scanning electron microscopy results. Contact angle measurements reveal that upon SRI irradiation the hydrophilic electrolyte membranes turn hydrophobic. High electrochemical stability window of -3.9 V to 6.5 has been achieved at the highest ion alma. of 1 x 10(12) ions cm(-2). Upon SRI irradiation the rate of decrease of ionic conductivity becomes slower indicating enhancement in interfacial stability. 2013 Elsevier B.V. All rights reserved