Experimental studies on poly methyl methacrylate based gel polymer electrolytes for application in electrical double layer capacitors

Studies have been carried out on gel polymer electrolytes comprising poly methyl methacrylate (PMMA)-ethylene carbonate (EC)–propylene carbonate (PC)–salts, LiClO4, NaClO4 and (C2H5)4NClO4 (TEAClO4) with a view to using them as electrolytes in electrical double layer capacitors (EDLCs) based on activated charcoal powder electrodes. The optimum composition of gel electrolytes, PMMA (20 wt%)–EC : PC (1 : 1 v/v)–1.0 M salts exhibit high ionic conductivity of the order of ~10−3 S cm−1 at room temperature with good mechanical/dimensional stability, suitable for their application in EDLCs. The EDLCs have been characterized using linear sweep cyclic voltammetry, galvanostatic charge–discharge tests and ac impedance spectroscopy. The values of capacitance of 68–151 mF cm−2 (equivalent to single electrode specific capacitance of 38–78 Fg−1 of activated charcoal powder) have been observed. These values correspond to a specific energy of 5.3–10.8 Wh kg−1 and a power density of 0.19–0.22 kW kg−1. The capacitance values have been observed to be stable up to 5000 voltammetric cycles or even more. A comparison of studies shows the predominant role of anions of the gel electrolytes in the capacitive behaviour of EDLCs.