Solid polymer electrolytes III: Preparation, characterization, and ionic conductivity of new gelled polymer electrolytes based on segmented, perfluoropolyether-modified polyurethane

New segmented polyurethanes with perfluoropolyether (PFPE) and poly(ethylene oxide) blocks were synthesized from a fluorinated macrodiol mixed with poly(ethylene glycol) (PEG) in different ratios as a soft segment, 2,4-toluene diisocyanate as a hard segment, and ethylene glycol as a chain extender. Fourier transform infrared, NMR, and thermal analysis [differential scanning calorimetry and thermo-gravimetric analysis (TGA)] were used to characterize the structures of these copolymers. The copolymer films were immersed in a liquid electrolyte (1 M LiClO₄/propylene carbonate) to form gel-type electrolytes. The ionic conductivities of these polymer electrolytes were investigated through changes in the copolymer composition and content of the liquid electrolyte. The relative molar ratio of PFPE and PEG in the copolymer played an important role in the conductivity and the capacity to retain the liquid electrolyte solution. The copolymer with a 50/50 PFPE/PEG ratio, having the lowest decomposition temperature shown by TGA, exhibited the highest ionic conductivity and lowest activation energy for ion transportation. The conductivities of these systems were about 10^-3 S cm^-1 at room temperature and 10^-2 S cm^-1 at 70 °C; the films immersed in the liquid electrolyte with an increase of 70 wt% were homogenous with good mechanical properties.