Poly(ethylene oxide) LiN(SO2CF2CF3)2 polymer electrolytes -: IV.: Raman characterization

The present report describes a Raman spectroscopy investigation of polymer electrolytes based on poly(ethylene oxide) (PEO)-lithium bis(perfluoroethylsulfonyl)imide (LiBETI), LiN(SO2CF2CF3)(2). A wide range of ether oxygen/salt, EO/LiBETI, molar ratios extending from 2 to 50 was considered. The crystalline salt was also investigated and a preliminary assignment of the Raman peaks of the salt, pure and dissolved in PEO, is made. The analysis of the Raman spectra supports the suggested formation of a solvent-separated P(EO)(6(or7))-LiBETI crystalline solvate. The highest conductivities of polymer electrolytes reported in previous works were for those electrolytes having compositions close to this solvate stoichiometry. The appearance of broad vibrational bands associated with amorphous PEO, even in very salt-diluted samples, confirms the ability of the BETI- anion to strongly affect the polymer morphology. (C) 2003 The Electrochemical Society.