A method based on impedance spectroscopy to determine transport properties of polymer electrolytes

In this work, we introduce a method based on impedance spectroscopy and the equations developed to evaluate, with a good degree of accuracy, the number density, mobility and diffusion coefficient of mobile ions. Nyquist plots of electrolytes based on poly(acrylonitrile) or PAN and methyl cellulose (MC) incorporated with lithium bis(oxalato) borate have been established from impedance measurements. Equivalent circuits based on a resistor and "leaky capacitor(s)" have been determined and the relevant impedance equations derived. The values of the parameters required in the equation are obtained from the Nyquist plots and the parameters that cannot be obtained from the respective plots have been obtained by trial and error in order to fit the Nyquist plots. The transport parameters are calculated using the developed equations and the results have been compared with those obtained from the broadband dielectric response (BDR) method. Finally, Fourier transform infrared (FTIR) spectroscopy has been used to verify the results obtained from the two approaches at room and elevated temperatures.