High-rate supercapacitive performance of GO/r-GO electrodes interfaced with plastic-crystal-based flexible gel polymer electrolyte

We report the performance of symmetrical electric double layer capacitors (EDLCs) fabricated with graphene oxide (GO) and reduced graphene oxide (r-GO) electrodes, and plastic crystal based flexible gel polymer electrolyte (GPE) film. The GPE, comprising the solution of lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) in a plastic crystal succinonitrile (SN) entrapped in poly (vinylidinefluoride-co-hexafluoropropylene) (PVdF-HFP), shows suitability as separator/electrolyte in EDLCs due to its excellent electrochemical properties including high ionic conductivity (similar to 1.97 x 10(-3) S cm(-1) a 20 degrees C). The GO and r-GO electrodes exhibit supercapacitive properties with the SN-based GPE as evidenced from electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and galvanostatic charge-discharge analyses. The residual oxygen functionalities associated with GO-electrodes provide additional pseudo-capacitance resulting in higher specific capacitance and specific energy (similar to 66 F g(-1) and 18 Wh kg(-1), respectively) as compared to r-GO electrodes (specific capacitance similar to tau(0) F g(-1) and specific energy similar to 15.6 Wh kg(-1)). High knee frequency f(k) (similar to 38 Hz), low response time similar to tau(0) (similar to 166.5 ms) and high pulse power P-0 (similar to 32.9 kW kg(-1)), observed from EIS studies, indicate the high rate capability of GO-electrodes-based EDLCs. About three fold increase in f(k) and three times decrease in tau(0) indicates a substantially higher rate performance of r-GO-based EDLCs with respect to GO-based cell. The high rate capability of GO/r-GO electrodes in combination with SN-based GPEs is further confirmed from the rectangular CV shapes up to scan rates of 5 V s(-1) for GO and 10 V s(-1) for r-GO electrodes. The r-GO based EDLC offers higher specific power (similar to 54.9 kW kg(-1)) as compared to that of GO-based EDLC (similar to 33.3 kW kg(-1)), as observed from charge-discaharge studies. Both EDLCs show stable capacitive performance up to similar to 11000-13500 charge-discharge cycles. (C) 2015 Elsevier Ltd. All rights reserved.