Vibrational and impedance spectroscopic analyses of semi-interpenetrating polymer networks as solid polymer...

Semi-interpenetrating polymer networks (semi-IPNs) with significant ionic conductivity (10^-4 S cm^-1 at ambient temperature) were studied by vibrational and impedance spectroscopies coupled with advanced analysis procedures. Vibrational spectroscopy recognized the numbers of free ions, ion pairs, ion-polymers and hydrogen bonds within the solid polymer electrolyte matrices (SPE). Electrochemical impedance spectroscopy (EIS) was used to quantify the bulk resistance and bulk relaxation time. The analyses used discrepancy-complexity plots to assess the number of free parameters properly, and EIS was further analyzed using impedance spectroscopy genetic programming (ISGP). Four compositions of PEO-polyurethane/poly(ethylene glycol) dimethyl ether (PEO-PU/PEGDME) were examined with LiClO₄ salt. The polymer electrolyte composition of 30/70 PEO-PU/PEGDME resulted in the lowest relaxation times and the highest ionic conductivity. The best salt concentration was observed at an EO/Li ratio of 30 for the PEO-PU/PEGDME : LiClO₄ (30/70) semi-IPN matrix. Several lithium salts of different anions were examined at an EO/Li ratio of 10, and the ionic conductivity achieved varied in the order -N(CF₃SO₂)₂^- > -ClO₄^- > -(CF₃SO₃)^- > -I^-/I₃^-.