A new kind of nanocomposite polymer electrolyte (NCPE) was prepared by addition of alumina nanoparticles into the polymer electrolyte that was plasticized with room temperature ionic liquid, N-ethyl-N'-methylimidazolium tetrafluoroborate (EMIBF₄). It was characterized by differential scanning calorimetry (DSC), X-ray diffraction (XRD), thermogravimetric analysis (TGA) and electrochemical impedance spectroscopy (EIS). The results show that the crystallinity of NCPE decreases with increase of the number of alumina nanoparticles. Its conductivity increases with the number of the nanopartilces firstly, and then decreases with further addition of the nanoparticles. The ionic conductivity reached the maximal value of 1.25×10^－3 S•cm^－1 at room temperature when the mass fraction of the nanoparticles was 10%.

Key words: polymer electrolyte, ionic liquid, alumina nanoparticle, poly(vinylidenefluoride-co-hexa- fluoropropylene)