A new group-contribution model based on the modified double-lattice theory with the free volume effect is developed and applied to describe phase-behaviors of solid polymer electrolyte/salt system with various pressures. The proposed group-contribution model includes the van der Waals energy contribution from dispersion and polar forces. Our result show that an eutectic point moves toward higher T-m and lower weight fraction of salt with increasing pressure. Quantitative description according to the proposed model is in good agreement with the experimentally observed transition temperature of a given system. (c) 2005 Elsevier Ltd. All rights reserved.