State-of-the-art poly(ethylene oxide) (PEO)-based polymer electrolytes have a t(Li+) much lower than 1; it is typically around 0.2-0.3. Thus, the development of single-cation-conductive, solvent-free polymer electrolytes is considered of prime importance for the progress of the technology of lithium batteries. Attempts mainly directed at immobilization of the anion in the polymer architecture have been reported in the past, but with only modest success because this approach generally depresses the conductivity to unacceptably low values. In this work, we report an alternative, new approach based on the addition to the PEO-LiX blend of an anion-trapping supermolecular component. In this way, polymer electrolytes with unity values of t(Li+) but still maintaining a true solid configuration combined with appreciable conductivity have been obtained. To our knowledge, this strategy has never been used, and we believe that this breakthrough result is associated with the immobilization of the anion (X-) by the additive and, possibly, by an ordering of the PEO-LiX system. (C) 2004 The Electrochemical Society.