A thin film of Ni nanocone arrays loaded with MnO2 nanostructures is prepared by an electro-deposition process and peeled off from the carrier substrate. This electrode shows superior performance for micro-supercapacitors.

To meet the rapidly growing demand, it is necessary to develop novel flexible energy storage devices with a high energy density in a limited area, a fast charging ability, a low cost for mass production and a miniaturized device size. To address the above issues, here we introduce the co-electro-deposition strategy, which is able to prepare an electrode material with a high areal capacitance (1670 mF cm À2 at 0.5 mA cm À2 ), a high areal mass (8.5 mg cm À2 ), an excellent mechanical robustness, a high through-put and great convenience even on a piece of a ubiquitous stainless steel mesh current collector. Based on this advancement, we are able to obtain an ultrathin (less than 200 mm) aqueous asymmetric supercapacitor device with a high energy density (1.8 Â 10 À3 W h cm À3 ), a high power density (0.38 W cm À3 at 3.62 Â 10 À4 W h cm À3 ) and an excellent rate capability. This energy storage device is integrated into a prototype smart card to drive a light emitting diode (LED) indicator, which is charged for 5 seconds and can light up the indicator for more than 2 hours, demonstrating great promise in miniaturized novel flexible energy storage devices.

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