Wide potential window and high capacitance for flexible asymmetric supercapacitor based on Cu2Se nanobrush and hydrangea-like NiCo2O4 microspheres

Flexible asymmetric supercapacitor (FAS) has recently attracted increasing interest due to an application potential in wearable device. However, its relatively lower potential and capacitance are still limited practical applications, owing to the challenges in the rational combination of asymmetric electrode materials with sophisticated nanostructure. Herein, a kind of Cu2Se nanobrush cathode material was designed and synthesized, and delivered an enhanced capacitance of 425 F g−1 at 1.0 A g−1. In addition, an anode material of NiCo2O4 with hydrangea-like microspheres was also prepared by a simple hydrothermal method. The as-prepared electrode shows a much higher specific (areal) capacitance of 1128 F g−1 (3.8 F cm−2). A FAS was fabricated by Cu2Se cathode and NiCo2O4 anode on a Au-coated polyimide. As a result, the device exhibit a high potential window up to 1.8 V, high capacitance of 130.4 F g−1, and maximum energy density of 21.2 Wh kg−1 at a power density of 2.02 kW kg−1. Furthermore, the FAS shows good flexibility and can withstand bending at 0-90° while keeping electrochemical performance constant after 6000 cycles. Such an impressive FAS based on asymmetric electrode with nanostructure would be a promising candidate for using in wearable devices.