In view of the safety concerns and the requirements of high energy density lithium batteries, the room temperature ionic liquids (RTILs) are being investigated as suitable candidates to substitute organic electrolytes in polymer electrolytes. In this article, we report synthesis, characterization, and electrochemical properties of nanocomposite polymer electrolytes (NCPEs) comprising of a RTIL [n-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (BMITFSI)] and nano-sized ceramic fillers (SiO2, Al2O3 or BaTiO3) hosted in electrospun poly(vinylidene fluoride-co-hexafluoropropylene) [P(VdF-HFP)] membranes. The addition of BMITFSI and ceramic fillers in polymer electrolytes results in high ionic conductivity at room temperature. The cells prepared with BMITFSI and different NCPEs show good interfacial stability and oxidation stability at >5.5V with the highest value of 6.0V for the NCPE incorporating BaTiO3. The cell with the NCPE containing BaTiO3 delivers high initial discharge capacity of 165.8mAhg−1, which corresponds to 97.5% utilization of active material under the test conditions, and showed the least % capacity fade after prolonged cycling.