Supercritical carbon dioxide (scCO(2)) as a treatment medium has a possibility to realize excellent room temperature conductivity more than 10(-4)S/cm for polymer electrolytes in the dry state. In this study, a typical high ion-conductive polyether-based electrolyte which consists of poly-[ethylene oxide-co-2-(2-methoxyethoxy)ethyl glycidyl ether] (P(EO/EM)) and lithium perchlorate (LiClO(4)) was used as a model sample for the scCO(2) treatment. We found the suitable scCO(2) treatment conditions (pressure, temperature and time) for high conductivity. The conductivity of sample treated at 7.5 MPa and 40 degrees C for 40 min was more than 100-times higher than that of original without the treatment, and the value decreased only 20% after 30 days. DSC measurement revealed that the decrease in glass transition temperature (T(g)) is caused by the scCO(2)-treatment. The change of ionic association in the scCO(2)-treated samples was confirmed using FT-IR measurement. The scCO(2) treatment gave rise to increase in peak fraction of free ClO(4)(-) anions (620-625 cm(-1)) and peak shift of upsilon(C-O-C) mode to lower frequency region (1060-1070 cm(-1)) depending on ether-Li(+) interactions. (C) 2011 Elsevier Ltd. All rights reserved.