Electrochemical redox supercapacitors using PVdF-HFP based gel electrolytes and polypyrrole as conducting polymer electrode

Electrochemical redox supercapacitors have been fabricated using polymeric gel electrolytes polyvinylidene fluoride co-hexafluoropropylene (PVdF-HFP)-ethylene carbonate (EC)-propylene carbonate (PC)-MClO4: M=Li, Na, (C2H5)(4)N and electrochemically deposited polypyrrole as conducting polymer electrode. The performance of the capacitors have been characterized using a.c impedance spectroscopy, cyclic linear sweep voltammetry and galvanostatic charge-discharge techniques. The capacitors shows larger values of overall capacitance of about 14-25 mF cm(-2) (equivalent to a single electrode specific capacitance of 78-137 F g(-1) of polypyrrole), which corresponds to the energy density of 11-19 W h kg(-1) and power density of 0.22-0.44 kW kg(-1). The values of capacitance have been found to be almost stable up to 5000 cycles and even more. A comparison indicates that the capacitive behaviour and the capacitance values are not much affected with the size of cations of the salts incorporated in gel electrolytes, rather predominant role of anions is possible at the electrode-electrolyte interfaces. Furthermore the coulombic efficiencies of all the cells were found to be nearly 100% that is comparable to the liquid electrolytes based capacitors. (c) 2006 Elsevier B.V. All rights reserved.