Development of polyacrylonitrile-based polymer electrolytes incorporated with lithium bis(trifluoromethane)sulfonimide for application in electrochromic device

In this study, polyacrylonitrile (PAN) as a polymer host is added with varying contents of lithium bis(trifluoromethane)sulfonimide (LiTFSI) as source of lithium (Li⁺) ions to form polymer electrolyte (PE) films. Dimethylformamide (DMF) is employed as the solvent. The electrical and structural properties of the PAN-based electrolytes are investigated by electrochemical impedance spectroscopy (EIS), Fourier transform infrared (FTIR) spectroscopy, and X-ray diffraction (XRD). The PE film containing 40 wt. % of LiTFSI is found to exhibit the best ambient conductivity of 2.54 × 10⁻⁴ S cm⁻¹ and the lowest degree of crystallinity. Investigation by FTIR spectroscopy has shown that PAN⋯DMF and DMF⋯Li⁺ interactions have occurred in the PAN-DMF-LiTFSI complexes. From XRD analysis, the films are found to be more amorphous with increasing LiTFSI contents. An electrochromic device is fabricated in the configuration of glass|ITO|WO₃|electrolyte|CeO₂-TiO₂|ITO|glass, and the cathodic coloration and anodic bleaching of WO₃ are found to occur at around −1.25 V and −0.40 V, respectively.