Toward wearable electronics: A lightweight all-solid-state supercapacitor with outstanding transparency, foldability and breathability

Wide applications of smart wearable electronics have triggered tremendous needs for energy storage devices featuring lightweight, transparency, foldability and breathability. However, conventional supercapacitor electrodes are always substrate-supported with a compact film structure, which strongly limits their air permeability, flexibility and transparency. In this report, we demonstrate the use of a freestanding, ultrathin (similar to 6 mu m), highly conductive (4 x 10(5) S/m), highly transparent (> 91%), air permeable (2600 mm/s at 10 Pa) and foldable metallic mesh electrode, decorated with active MnO2 microstructures, as a breathable, transparent and foldable supercapacitor electrode. By introducing Au nanoparticles as the nanoglue between Ni and MnO2, excellent electrochemical performances including large areal capacitance (268 mF/cm(2)) and high cycling stability (90.1% capacitance retention after 10000 cycles) are obtained in the MnO2-Au-Ni mesh electrode. Furthermore, the assembled all-solid-state supercapacitor device delivers high optical transparency (similar to 83.6%), high air permeability (45.4 mm/s at 100 Pa), superior electrochemical performances and can withstand various deformations including bending, folding, and crumpling. The present freestanding mesh structure electrode could be further explored and applied in more potential applications, such as ion batteries, wearable sensors, and conformal healthcare devices.