A homogeneous, composite polymer electrolyte (PE) containing poly(ethylene oxide) (PEO), CF3SO3Li and 33 wt.% of aluminum carboxylate [RC(O)OAlEt2](2) with an oligooxyethylene group R = CH2CH2C(O)O(CH2CH2O)(n),CH3 (n = 7) (AlCarb7), characterized by low glass transition temperature T-g = 51.4 degrees C was prepared. The interaction of aluminum carboxylate with various lithium salts was characterized on the basis of Al-27 NMR spectroscopy in CDCl3 solutions. The bulk conductivity of solid PE with AlCarb7 is of the order of 10(-5)S cm(-1) at 60 degrees C and 10(-4) S cm(-1) at 90 degrees C. Electrochemical tests of Li vertical bar PE vertical bar Li cells showed a decrease in the R-SEI with temperature, stabilizing at about 10 Omega cm(-2). The lithium ion transference numbers determined by ac-dc polarization experiments range from 0.7 to 0.9. Li-7, F-19 and (1) H NMR spectra, the relaxation time and diffusion data were obtained. The calculated lithium transference number t(+) at 50 degrees C is equal to 0.995, which suggests practically complete immobilization of the triflate salt anions. In the range of high temperatures (130-180 degrees C) t, is equal 0.35-0.39. The dependence of t, on temperature should probably be connected with the partial dissociation of the aluminum carboxylate and lithium salt complex. (c) 2007 Elsevier B.V. All rights reserved.