Highly Rate Capable Nanoflower-like NiSe and WO₃@PPy Composite Electrode Materials toward High Energy Density Flexible All-Solid-State Asymmetric Supercapacitor

An advanced novel all-solid-state asymmetric supercapacitor (ASC) device of high energy and power densities is designed on the basis of the nanoflower-like NiSe as the positive electrode and WO3@PPy composite as the negative one. The porous NiSe was prepared by facile selenization of predesigned NiO nanoflowers, and the WO3@PPy composite was synthesized through in situ oxidative polymerization of pyrrole in the presence of dispersed WO3 nanosticks which, in turn, was produced by a simple sulfate-assisted hydrothermal method. When tested as a supercapacitor positive electrode in the three-electrode system, the NiSe exhibits an appreciably higher specific capacitance of 1274 F g–1 at 2 A g–1 than that of the NiO nanoflower (774 F g–1). Again, as the negative electrode, the WO3@PPy composite also shows excellent electrochemical properties with a higher specific capacitance (586 F g–1 at 2 A g–1) than those of either of its components (WO3: 402 F g–1 and PPy: 224 F g–1). Based on these properties of the respective electrodes, a flexible ASC device was designed and fabricated by assembling the NiSe as the positive electrode with WO3@PPy composite as the negative electrode. The NiSe//WO3@PPy solid-state ASC with an extended potential window of 1.25 V demonstrates an admirable energy density of 37.3 Wh kg–1 at a power density of 1249 W kg–1 at 2 A g–1 along with outstanding long-term cycling stability that retains 91% of the initial capacitance even after 5000 charging and discharging cycles. All these results reveal the proficiency of the ASC device as a high-performance energy storage system for next-generation portable electronics.