Phase behavior and ion conductivity of electrolytes based on aggregating combshaped polyethers

Abstract

The influence of temperature and salt concentration on the properties of solid polymer electrolytes based on lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) complexed by combshaped polyethers has been studied. The combshaped polyethers consisted of styrenic backbone polymers carrying pendant poly(ethylene oxide) (PEO) or poly(ethylene oxide- co-propylene oxide) (PEOPO) side chains terminated by hydrocarbon (C 16) chain ends. Analysis by DSC and polarized light microscopy showed that the structure and composition of the side chains had a large effect on the crystallization behavior of the electrolytes. For example, a slow crystallization process was noted in electrolytes containing PEO side chains after storage at ambient temperature. This transition was not observed in corresponding electrolytes containing PEOPO side chains. Polymer aggregation by phase separation of the hydrocarbon chain ends was indicated in all electrolytes by narrow melt endotherms. A maximum conductivity of 10 −4.6 S/cm at 20°C, and 10 −3.2 S/cm at 80°C, was found at [Li]/[O]=0.050 for an electrolyte based on a polyether having side chains containing 20 wt% propylene oxide. The temperature dependence of the ionic conductivities was well described by Vogel–Tamman–Fulcher equations in the absence of crystallinity.