The supplementary material includes Note 1: Air-photonics THz spectrometer; Note 2: Data
analysis for the ultrabroadband THz spectroscopy; Note 3: Transport parameters of PEO-based
SPEs; Note 4: Attenuated Total Reflectance (ATR)-FTIR spectroscopy; Note 5: Temperaturedependent
FTIR spectroscopy; Note 6: Schematic illustration of anharmonic and harmonic
potentials; Note 7: Microscopic image of samples.