Lithium complex with C=N group of polyacrylonitrile (PAN) in the PAN-based electrolyte plasticized (7.5 wt% of the total weight) with binary mixture, ethylene carbonate (EC) and propylene carbonate (PC) are present. At low salt concentration, lithium is exchanged rapidly between the polymer substrate and the EC/PC mixture. But with increasing salt content the electrolyte viscosity increases, and the formation of a weak complex between lithium ion and the CN group in PAN is observed. Sudden increase in the Li-7 chemical shifts substantially broadened line-width in Li-7 NMR and the two-fold increase of the activation energy in variable temperature (LiT1)-Li-7 relaxation measurements indicated clear presence of the complex. However, the conductivity is not substantially decreased with the appearance of the complex. The result suggested that the ion transport through the more direct lithium site-jump along the polymer chain is equally effective as the ion diffusion through the EC/PC solvent. (C) 2001 Elsevier Science Ltd. All rights reserved.