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

Abstract

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≥PANP(VdF-HFP)≥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.