Characterization of Lithium Ion-Conducting Blend Biopolymer Electrolyte Based on CH-MC Doped with LiBF4

Lithium ion-conducting polymer blend electrolytes based on chitosan and methylcellulose complexed with lithium tetrafluoroborate (LiBF4) were prepared by a solution-casting method. The features of complexation of the solid polymer electrolytes were studied using X-ray diffraction techniques. Electrical conductivity of the prepared films was measured as a function of frequency at a different temperature. The increased trend of the electrical conductivity with increasing temperature and salt concentration can be attributed to increasing the mobility and number of lithium ions, respectively. The polymer electrolyte system exhibited Arrhenius-type, temperature-dependence ion conductivity behavior. Optical properties such as optical band gap, tail due to localized states and complex refractive index were estimated for present polymer electrolyte system from optical absorption measurement in the wavelength region 190-1100 nm. It was found that the optical direct band gap values shifted to lower energies upon addition of LiBF4 salt up to 40 wt% dopant concentration, and showed an increasing tendency for a further increase in dopant concentration. The high refractive index for this composition (2.44-2.63) at visible wavelengths eminently suitable for optical applications.