Performance of gel-type polymer electrolytes according to the affinity between polymer matrix and plasticizing solvent molecules

The solvent retention ability, mechanical strength, and sub-ambient temperature conductivity of polymer gel electrolytes is investigated on the basis of polymer-solvent affinity. Four different polymers, poly(vinylidene fluoride) (PVdF), poly(vinylidene fluoride) (PVdF)-hexafluoropropylene (HFP) copolymer, poly(acrylonitrile) (PAN) and poly(methyl methacrylate) (PMMA) are employed as the gel-forming polymer matrix, while ethylene carbonate (EC)/propylene carbonate (PC) is used as the plasticizing solvent. The solvent retention ability of polymer gels decreases in the order of PMMA greater than or equal to PAN much greater than P(VdF-HFP) greater than or equal to PVdF, which is surely the relative order of polymer affinity for the solvent. The low affinity polymers are advantageous in respect of the mechanical strength of polymer gels, where there appears a microscopic phase separation between the polymer- and solvent-rich phases. For the low temperature conductivity, however, the high affinity polymers are preferred as the freezing of solvent molecules is retarded by virtue of stronger polymer-solvent interactions. When a high affinity polymer is blended with a low affinity one, the features that are intermediate between two extremes are observed. (C) 2001 Elsevier Science Ltd. All rights reserved.