Won-Gil Lee

Highly Flexible and Planar Supercapacitors Using Graphite Flakes/Polypyrrole in Polymer Lapping Film.

Flexible supercapacitor electrodes have been fabricated by simple fabrication technique using graphite nanoflakes on polymer lapping films as flexible substrate. An additional thin layer of conducting polymer polypyrrole over the electrode improved the surface conductivity and exhibited excellent electrochemical performances. Such capacitor films showed better energy density and power density with a maximum capacitance value of 37 mF cm(-2) in a half cell configuration using 1 M H2SO4 electrolyte, 23 mF cm(-2) in full cell, and 6 mF cm(-2) as planar cell configuration using poly(vinyl alcohol) (PVA)/phosphoric acid (H3PO4) solid state electrolyte. Moreover, the graphite nanoflakes/polypyrrole over polymer lapping film demonstrated good flexibility and cyclic stability.

Enhanced supercapacitive performances of functionalized activated carbon in novel gel polymer electrolytes with ionic liquid redox-mediated poly(vinyl alcohol)/phosphoric acid

Supercapacitors with solid/gel polymer electrolytes have attracted much attention due to their high reliability, flexibility, facile designing, being separator-free and free from electrolyte leakage and volatilization such that they can meet the increasing demands of practical applications. The present work reports on a functionalized activated carbon (AC) supercapacitor based on novel redox-mediated gel polymer electrolyte, PVA/H3PO4/ionic liquid (1-ethyl-3-methylimidazolium tetrafluoroborate, [EMIM]BF4). The electrochemical properties of this supercapacitor were studied using cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectroscopy techniques with various concentrations of [EMIM]BF4 in PVA/H3PO4 gel polymer electrolyte. The incorporation of [EMIM]BF4 in PVA/H3PO4 electrolyte effectively increased the specific capacitance value due to the improved ionic conductivity and additional pseudo-reaction occurring in the electrode/electrolyte interfaces. The specific capacitance of the supercapacitor using PVA/H3PO4/[EMIM]BF4 (50%) electrolyte showed a maximum value of 271 F g−1 at 0.5 A g−1 discharge current, which is much higher than the bare PVA/H3PO4 (103 F g−1) based supercapacitor. The supercapacitor with PVA/H3PO4/[EMIM]BF4 (50%) electrolyte showed enhanced energy and power density of 54.3 W h kg−1 and 23.88 kW kg−1 respectively. Moreover the device showed comparable specific capacitance retention after 3000 cycles of charge/discharge.

Rationally designed spider web-like trivanadium heptaoxide nanowires on carbon cloth as a new class of pseudocapacitive electrode for symmetric supercapacitors with high energy density and ultra-long cyclic stability

The design and construction of one-dimensional (1D) nanostructures on flexible electrodes without the use of polymer binders/conductive additives has shown great potential for engineering improved electrochemical properties in supercapacitors. Herein, a facile in situ hydrothermal technique was adopted for the growth of trivanadium heptaoxide nanowires on carbon fiber cloth (V3O7/CFC). The resultant V3O7 sample displayed the self-accumulated growth of nanowires on CFC after 48 h with a spider web-like morphology. The specially designed binder-free V3O7/CFC was used to fabricate a symmetric supercapacitor in aqueous 1 M Na2SO4 electrolyte, which showed excellent electrochemical performance. Specifically, in the half-cell configuration, the device exhibited a maximum specific capacitance (Csp) of 198 F g−1 at 1 A g−1 and in full-cell configuration, it showed a Csp of 151 F g−1 at the same current density with ultra-high cycling stability of ∼97% (after 100 000 cycles). In addition, the performance of the symmetric device in 1 M 1-ethyl-3-methylimidazolium trifluoromethanesulfonate electrolyte was studied and it showed a wide potential window of 2 V with a maximum Csp of 178 F g−1. Furthermore, the device exhibited high energy and power densities of 24.7 W h kg−1 (48.5 mW h cm−2) and 5.13 kW kg−1 (10.05 W cm−2), representing as a viable electrode in ionic liquid electrolyte.