Thermal, electrochemical, and spectroscopic characterizations of hyperbranched polymer electrolyte

Novel polymer electrolytes have been prepared with hyperbranched polymers as the host and lithium trifluoromethanesulfonimide, LiN(CF3SO2)(2), as the ion source. Analysis of the salt concentration dependence of the glass transition temperature indicates that intermolecular interactions occur in the polymer electrolytes and that these hyperbranched polymers can function as a "solvent" for the lithium salt. Two maxima were observed in the isotherm of conductivity vs. the lithium salt concentration in the polymer electrolyte by ac impedance measurements. Fourier transform infrared spectroscopic analysis of the polymer electrolytes over a large range of lithium salt concentration has been made. It is shown that these two conductivity maximas might be related to the Li+-polymer coordination at low lithium salt concentration and the formation of ion pairs and higher ion aggregates at high lithium salt concentration, respectively. (C) 1999 The Electrochemical Society. An rights reserved.