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.

Lithium ion conducting polymer electrolytes based on polyacrylonitrile (PAN) and lithium bis(oxalato)borate (LiBOB) have been prepared and characterized. The polymer electrolytes having PAN:LiBOB weight ratios of 90:10, 80:20, 70:30, 60:40 and 50:50 were prepared using dimethylformamide as solvent. The electrolyte having the composition 50 wt.% PAN–50 wt.% LiBOB shows the highest room temperature conductivity of 2.55 × 10−5 S cm−1. This sample demonstrated a lithium ion transference number of 0.25 and a breakdown voltage of 1.6 V. The highest conducting electrolyte was then sandwiched between two symmetrical carbon electrodes to fabricate an electrical double layer capacitor (EDLC). The EDLCs were characterized using impedance measurement, cyclic voltammetry (CV) and galvanostatic charge–discharge tests. The capacitance obtained from impedance measurement is about 35 F g−1 at frequency 10 mHz. From CV, the capacitance is calculated to be 24 F g−1 at 10 mV s−1 scan rate. The discharge capacitance of the EDLCs is determined in the range from 22 to 10 F g−1 at corresponding discharge currents from 0.2 to 1.5 mA, respectively. This also corresponds to a specific energy from 3.01 to 1.47 W h kg−1 and a specific power from 380 to 474 W kg−1, respectively. Copyright © 2013 John Wiley & Sons, Ltd.