Nanocomposite polymer electrolytes (NCPEs) composed of poly(ethylene oxide), calcium phosphate [Ca3(PO4)2], and lithium perchlorate (LiClO4)/lithium bis(trifluoromethane sulfonyl)imide [LiN(CF3SO2)2 or LiTFSI] in various proportions were prepared by a hot-press method. The membranes were characterized by scanning electron microscopy, differential scanning calorimetry, thermogravimetrydifferential thermal analysis, ionic conductivity testing, and transference number studies. The free volume of the membranes was probed by positron annihilation lifetime spectroscopy at 30 degrees C, and the results supported the ionic conductivity data. The NCPEs with LiClO4 exhibited higher ionic conductivities than the NCPE with LiTFSI as a salt. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012