We develop a facile one-step hydrothermal method to directly grow interconnected Co0.85Se nanosheets
on nickel foam as electrode for supercapacitors. The Co0.85Se electrodes exhibit a high specific capacitance
(1528 F g-1 at 1 A g-1 and 715 F g-1 at 20 A g-1), excellent cycling stability (92% retention after 5000
cycles) and good conductivity. Moreover, an asymmetric supercapacitor (ASC) is fabricated using Co0.85Se
nanosheets as the positive electrode and active carbon (AC) as the negative electrode. The ASC also
exhibits excellent electrochemical performance with high energy density (~45 Wh kg1), high power
density (16 kW kg-1) and remarkable cycling stability (~10.9% loss after 5000 cycles). Furthermore, two
ASCs connected in series are capable of lighting a red LED at least for 5 min after being charged for only
15 s to 3.2 V. This work demonstrates that the interconnected Co0.85Se nanosheets with threedimensional
porous structures are promising electrodes for high-performance supercapacitors with
large energy density.