Suitability of natural rubber-based polymer electrolyte for energy storage

Abstract

Electrochemical double-layer capacitor (EDLC) is an evolving member in the energy storage movement which really plays a major part in satisfying the power demands of electronic devices and systems. Today, a substantial interest is paid on environmental friendly, cheap and safe devices in the modern world. Therefore, the present study was carried out to fabricate EDLCs using natural rubber-based solid polymer electrolytes (SPEs) and exfoliated graphite electrodes which possess many of those requirements. Electrolyte was prepared using ammonium trifluoromethanesulfonate (NH4CF3SO3–NH4TF) as the salt, titanium dioxide (TiO2) as a nano additive, propylene carbonate (PC) as a solvent and 49 methyl groups grafted natural rubber (MG49) as the polymer. First, electrolytes having different salt compositions were prepared using solvent casting method. Minced NR was dissolved in tetrahydrofuran (THF) using magnetic stirring. NH4TF solution was prepared separately. MG49 and NH4TF solutions were then mixed together and stirred further. It was then poured into caped petri dish and the solvents were left to slowly evaporate. This procedure was repeated several times for different salt compositions. The optimised composition was found as NR:0.4 NH4TF (by weight basis) having a room temperature conductivity of 3.82 × 10–4 S/cm. TiO2 and PC were added to this optimised composition to enhance the conductivity. The highest room temperature conductivity obtained was 7.10 × 10–4 S/cm for the composition, NR:0.4 NH4TF:10%PC:10%TiO2. Exfoliated graphite electrodes were prepared using natural graphite. The characterisation of EDLC was done by using electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and galvanostatic charge discharge (GCD) test. Single electrode specific capacitance of the EDLC was found to be 1.68 F/g from CV test. Discharge capacitance was 0.78 F/g from the GCD test. Moreover, a good cyclic stability was observed. This novel natural rubber and natural graphite-based EDLC can be used as an energy storage device with further modifications.