High performance asymmetric supercapacitor based on polypyrrole/graphene composite and its derived nitrogen-doped carbon nano-sheets

Neutral aqueous medium is a promising electrolyte for supercapacitors because it is low-cost, environmental-friendly and can achieve rapid charging/discharging with high power density. However, the energy density of such supercapacitor is significantly limited by its narrow operational voltage window. Herein, we demonstrated an effective approach to broaden the operational voltage window by fabricating an asymmetric supercapacitor (ASC) with polypyrrole/reduced graphene oxide (PPy/rGO) composite and its derived Nitrogen-doped carbon nano-sheets (NCs) as positive and negative electrode material, respectively. The homogeneous nano-sheet and mesoporous structure of PPy/rGO and NCs can facilitate rapid charge/ion migration and provide more active sites for ions adsorption/exchange to improve their electrochemical performance. Benefiting from high capacitance and good rate performance of PPy/rGO and NCs electrodes, the as-fabricated ASCs devices in a polyvinyl alcohol/LiCl gel electrolyte can realize a wide operational voltage of 1.6 V and deliver high energy density of 15.8 wh kg−1 (1.01 mWh cm−3) at 0.14 kW kg−1 (19.3 mW cm−3), which still remains 9.5 wh kg−1as power density increases to 6.56 kW kg−1, as well as excellent long-term cycling stability with about 88.7% capacitance retention after 10000 cycles. The remarkable performances suggest that the ASCs devices are promising for future energy storage applications.