In situ nitrogen-doped carbon nano-onions for ultrahigh-rate asymmetric supercapacitor

The growing demand for clean energy storage and delivery during surge power applications motivate us to synthesize highly graphitic, mesoporous nitrogen-doped carbon nano-onions (N-CNOs) via a one-step in situ flame pyrolysis procedure for their potential asymmetric supercapacitor (ASC) electrodes. The operating voltage of the fabricated ASC device is extended to 1.8 V in a 1 M Na2SO4 electrolyte, yielding a maximum specific capacitance of 113 F g(-1) and a high energy density of 51 Wh kg(-1) at a current density of 4 A g(-1). Importantly, even at a high current density of 20 A g(-1), the device still delivers a high power density of 18 kW kg(-1) while maintaining an energy density of 6 Wh kg(-1). Furthermore, the novel ASC exhibits excellent electrochemical cyclic stability over 10,000 cycles, retaining 98% of its specific capacitance and excellent coulombic efficiency of 99% at a high current density of 20 A g(-1). The smaller characteristic relaxation time-constant (340 ms) than the previously reported graphene/MXene-based supercapacitors, validates the ultrahigh-rate ASC device-performance. These results confirm that N -CNOs can be used as a novel alternative electrode material in supercapacitors with high specific energy and power. (c) 2019 Elsevier Ltd. All rights reserved.