Quasi-Solid Semi-Interpenetrating Polymer Networks as Electrolytes: Part II. Assessing the Modes of Ion-Ion and Ion-Polymer Interactions Employing Mid-Fourier Transform Infrared Vibrational Spectroscopy

The present study is a detailed vibrational spectroscopy investigation on the ion ion and ion polymer interactions that exist post-solvation or complexation in a new class of quasi-solid polymer electrolytes. Fourier transformed infrared spectra of the synthesized semi-interpenetrating polymer networks (semi-IPNs) matrix of poly(ethyleneoxide) -polyurethane/poly(ethylene glycol) dimethyl ether (P4K-PU/P2 (30:70)) complexed with LiCF3SO3 and LiN(CF3SO2)(2) is deconvoluted for three primary stretching zones (ether, carbonyl, and amine) to isolate and identify the ionic species and polymer segments involved. The analysis revealed crucial information pertaining to the localized ion-association behavior, vital clues regarding the competitive interactions present, and important insights into the mechanisms of charge transport. The spectroscopic signatures imply favorable presence of positively charged triple ions or higher aggregate species along with a significant amount of free ions and a preferential solubility of the added electrolytes in the amorphous domains of the polymer. Critical salt concentrations C-c of EO/Li = 20 and EO/Li = 30 estimated for the LiTf and LiTFSI systems, respectively, are in good agreement with experimentally observed conductivity results. The appreciably high ionic conductivity in these semi-IPN systems could be effectively rationalized considering the nature of ionic dissociation, reassociation, and competitive interaction mechanisms. The availability of a highly disordered matrix with an optimal number of free sites, excellent segmental mobility, appreciable free volume, and finally the existence of adequate labile ionic species, all aids in the high charge transport observed in this new class of quasi-solid electrolytes.