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

Abstract

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 (∼1.97×10−3Scm−1 a 20°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 (∼66Fg−1 and 18Whkg−1, respectively) as compared to r-GO electrodes (specific capacitance ∼60Fg−1 and specific energy ∼15.6Whkg−1). High knee frequency fk (∼38Hz), low response time ∼τ0 (∼166.5ms) and high pulse power P0 (∼32.9kWkg−1), observed from EIS studies, indicate the high rate capability of GO-electrodes-based EDLCs. About three fold increase in fk and three times decrease in τ0 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 5Vs−1 for GO and 10Vs−1 for r-GO electrodes. The r-GO based EDLC offers higher specific power (∼54.9kWkg−1) as compared to that of GO-based EDLC (∼33.3kWkg−1), as observed from charge-discaharge studies. Both EDLCs show stable capacitive performance up to ∼11000-13500 charge-discharge cycles.