Improvement in flexibility and volumetric performance for supercapacitor application and the effect of Ni–Fe ratio on electrode behaviour

To increase the flexibility, volumetric capacitance and energy density of a supercapacitor, an economical but effective method of rolling a foam current collector before the direct growth of electrode materials on it is proposed and studied for the first time. By using this novel economic approach, volumetric capacitance and energy density are demonstrated to increase almost 3 times, even though they have not been optimized yet. At the same time, the flexibility is improved tremendously, making it possible to obtain an extremely flexible supercapacitor. Additionally, in the current work, the material system of nickel iron oxide has been studied systematically. The effect of nickel iron ratio on the electrochemical performance has been examined. The resulting extremely bendable or flexible current collector with the active material grown on it showed a high volumetric capacitance of 11.6 F cm super(-3) and energy and power densities of 4.12 mW h cm super(-3) and 236.25 mW cm super(-3), respectively. It should be noted that these volumetric values are truly high because they are calculated based on the whole device volume of the two current collectors, rather than that of the active material itself only. Such a strategy might be readily extended to other systems with nano-structured materials grown on metal foams.