Flexible three-dimensional nanoporous metal-based energy devices

A flexible three-dimensional (3-D) nanoporous NiF₂-dominant layer on poly(ethylene terephthalate) has been developed. The nanoporous layer itself can be freestanding without adding any supporting carbon materials or conducting polymers. By assembling the nanoporous layer into two-electrode symmetric devices, the inorganic material delivers battery-like thin-film supercapacitive performance with a maximum capacitance of 66 mF cm^-2 (733 F cm^-3 or 358 F g^-1), energy density of 384 Wh kg^-1, and power density of 112 kW kg^-1. Flexibility and cyclability tests show that the nanoporous layer maintains its high performance under long-term cycling and different bending conditions. The fabrication of the 3-D nanoporous NiF₂ flexible electrode could be easily scaled.