Compositional effect on the morphology and ionic conductivity of thermoplastic polyurethane based electrolytes

Four thermoplastic polyurethanes (TPUs) were synthesized from poly(ethylene glycol) (PEG), 4,4^′-methylenebis(phenyl isocyanate) (MDI), and 1,4-butanediol (1,4-BDO) with different 1,4-BDO/PEG ratios. The effect of polymer structure on the conductivity of the polymer elelctrolytes was investigated. Fourier transform infrared spectroscopy (FT-ir) and differential scanning calorimetry (DSC) were utilized to monitor changes in the morphology of the TPUs as polymeric solid electrolyte doped with LiClO₄. The structure of the TPUs has been investigated by 1H solution nuclear magnetic resonance spectroscopy. Alternating current (AC) impedance experiments were performed to determine the ionic conductivities of TPU films and their corresponding gel type electrolytes. The conductivity depends on the soft-segment concentration and on the degree of phase separation exhibited by these materials. One of the investigated TPU gel type electrolytes exhibits an ionic conductivity as high as 3×10⁻⁴ S/cm at room temperature.