Understanding of the ion transport in blended TPU-PEO polymer electrolytes

Fast and easily scalable solvent-free extrusion of polymer electrolytes would represent significant progress in the development of environmentally friendly solid alkali-ion and alkali-metal batteries. In this study, we compare cast and extruded solid polymer electrolytes composed of lithium bis(trifluoromethanesulfonyl)imide salt of varying content dissolved in host matrix of polyurethane and polyethylene oxide. The electrolytes were characterized by means of differential scanning calorimetry, infrared spectroscopy, AC impedance, broad-band spectroscopy, and one-dimensional ⁷Li and ¹⁹F nuclear magnetic resonance. Analysis of the FTIR spectra showed that both polymers can coordinate lithium cations by ethylene oxide (EO) and amine (NH) electron donating groups. The interactions between Li⁺ and each polymer affect phase transition behavior, conductivity, and ion self-diffusion coefficients. Contrary to our expectations, it was found that unidirectional annealing, which was assumed to be induced by the extrusion process, does not alter out-of-plane ionic conductivity. Moreover, the bulk conductivity of extruded blended polymer electrolyte with 1:15 Li:EO ratio is more than twice that of its cast counterpart over the entire temperature range studied.