Ultrathin and flexible power sources are essential for the rapid development of portable and wearable electronics. The deployment of 3-dimensional (3-D) nanostructured materials on the current collectors has recently emerged as a promising strategy for preparing high-performance supercapacitors. Additionally, it is equally important to develop an appropriate device packaging technique, so as to maximize the improvement of the electrode performance characteristic. Herein, we develop a simple and efficient method for fabricating ultrathin and flexible supercapacitor electrodes containing a manganese dioxide (MnO2) nanostructure deposited onto 3-D nickel nanocone arrays (NCAs). The MnO2-NCAs electrode was prepared by an electro-deposition technology, which involves the cathode deposition of NCAs on a titanium carrier film as the current collector and subsequent anode deposited from the MnO2 nanostructures as the active material. The electrode can be peeled off from the carrier film and thus the resulting freestanding electrode is as thin as 3 μm, and exhibits outstanding mechanical robustness, high specific capacitance (632 F g−1), enhanced energy density (52.2 W h kg−1) and excellent cycle performance (95.3% retention after 20000 cycles). We further fabricated ultrathin supercapacitors with a total thickness of ∼27 μm, which achieved unprecedented features including superior energy density by volume (2.7 × 10−3 W h cm−3), superior flexibility and reliability. We demonstrated the application of the MnO2-NCAs supercapacitor as an ultrathin power source such as driving a LED indicator. This technology may find vast applications in future wearable electronics.
