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

The influence of temperature and salt concentration on the properties of so lid polymer electrolytes based on lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) complexed by combshaped polyethers has been studied. The combshap ed polyethers consisted of styrenic backbone polymers carrying pendant poly (ethylene oxide) (PEO) or poly(ethylene oxide-co-propylene oxide) (PEOPO) s ide chains terminated by hydrocarbon (C-16) chain ends. Analysis by DSC and polarized light microscopy showed that the structure and composition of th e side chains had a large effect on the crystallization behavior of the ele ctrolytes. For example, a slow crystallization process was noted in electro lytes 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 ch ain ends was indicated in all electrolytes by narrow melt endotherms. A max imum conductivity of 10(-4.6) S/cm at 20 degreesC, and 10(-3.2) S/cm at 80 degreesC, was found at [Li]/[O] = 0.050 for an electrolyte based on a polye ther having side chains containing 20 wt% propylene oxide. The temperature dependence of the ionic conductivities was well described by Vogel-Tamman-F ulcher equations in the absence of crystallinity. (C) 2001 Elsevier Science Ltd. All rights reserved.