Novel pseudo-parallel activated carbon/carbon cloth electrodes connected in novel series for flexible symmetric supercapacitor with enlarged potential window

Wide potential window and high capacitance are required to achieve high energy and power densities for supercapacitors (SC). Potential window can be widened by applying ionic liquid electrolyte or establishing series connected devices. Due to high costs of ionic liquids, series connected device is more promising to achieve wide potential window especially for commercial uses. Although wider potential window can be generated by connecting more devices in series, numerous connected points between devices may increase charge-transfer resistance and reduce capacitance. In this work, a novel pseudo-parallel activated carbon/carbon cloth electrode (PPAC) connected in novel series (PNS) is proposed to assemble flexible symmetric SC. Activated carbon/gel electrolyte coated area to naked carbon cloth area in the electrode is optimized regarding to the ion adsorption/desorption sites and charge-transfer resistance. A wide potential window of 3 V and high capacitance of 1.8 F are achieved at 40 mV/s for the optimized PNS-assembled SC, which presents a maximum energy density of 20.6 Wh/kg at the power density of 1023.9 W/kg and excellent charge/discharge cycling stability with 90% capacitance retention after 2500 times charge/discharge process. The significance of PPAC design and novel series is emphasized by comparing the electrochemical performance with the devices without PPAC design or without novel series. Construction of PPAC in series is proved to be capable of widening the potential window and maintaining high capacitance. More complex designs based on PPAC is expected to develop soon for achieving effective energy storage and facile fabrication. (C) 2020 Elsevier Ltd. All rights reserved.