Effect of lithium thiocyanate addition on the structural and electrical properties of biodegradable poly(ε-caprolactone) polymer films

Polymer electrolyte films of biodegradable poly(ε-caprolactone) (PCL) doped with LiSCN salt in different weight ratios were prepared using solution cast technique. The effect of crystallinity and interaction between lithium ions and carbonyl groups of PCL on the ionic conduction of PCL:LiSCN polymer electrolytes was characterized by X-ray diffraction (XRD), optical microscopy, Fourier transform infrared spectroscopy (FTIR) and AC impedance analysis. The XRD results revealed that the crystallinity of the PCL polymer matrix decreased with an increase in LiSCN salt concentration. The complexation of the salt with the polymer and the interaction of lithium ions with carbonyl groups of PCL were confirmed by FTIR. The ionic conductivity was found to increase with increasing salt concentration until 15 wt% and then to decrease with further increasing salt concentration. In addition, the ionic conductivity of the polymer electrolyte films followed an Arrhenius relation and the activation energy for conduction decreased with increasing LiSCN concentration up to 15 wt%. UV–vis absorption spectra were used to evaluate the optical energy band gaps of the materials. The optical energy band gap shifted to lower energies with increasing LiSCN salt concentration.