Simultaneously achieving high energy and power density for ultrafast-charging supercapacitor built by a semi-graphitic hierarchical porous carbon nanosheet and a high-voltage alkaline aqueous electrolyte

How to simultaneously achieving high energy and power density is a key challenge for ultrafast-charging supercapacitors. Herein, a composite alkaline electrolyte with widened operation voltage is utilized to improve the energy density of aqueous supercapacitors, while a well-designed semi-graphitic hierarchical porous carbon nanosheet electrode material is prepared to ensure the high power density by effectively alleviating polarization during the charging/discharging process. The symmetrical supercapacitor built by the above electrode material and electrolyte exhibits both high energy and power density, which can reliably work at 1.3 V and display high capacitance retention of 85.0% at 50 A g−1. A high energy density of 12.2 Wh kg−1 is achieved at 203 W kg−1 and more than 85.0% of energy density is retained even when the power density increases by ca 100-fold (10.2 Wh kg−1 at 20.4 kW kg−1). The assembled supercapacitor can be charged to 100% within 3.4 s at 20 A g−1 and then deliver a specific capacitance of 48.9 F g−1 at a small discharging current density of 0.5 A g−1, which value reaches 93.1% of the specific capacitance recorded by using the same charging/discharging current density (0.5 A g−1), indicating the reliable ultrafast-charging performance in practical application. [Display omitted] •A well-designed semi-graphitic hierarchical porous carbon nanosheet is prepared.•Supercapacitor can reliably work at 1.3 V in a new-developed composite electrolyte.•High energy and power density are simultaneously achieved.•A high energy density of 12.2 Wh kg−1 is achieved at 203 W kg−1.•85.0% of energy density is retained when power density is increased by 100-fold.