Flexible Hybrid Supercapacitor Achieving 2.2 V with NiCo2S4/Polyaniline/MnO2 and N, S‐Co‐Doped Carbon Nanofibers for Ultra‐High Energy Density

Abstract Flexible all‐solid‐state asymmetric supercapacitors (FAASC) represent a highly promising power sources for wearable electronics. However, their energy density is relatively less as compared to the conventional batteries. Herein, a novel ultra‐high energy density FAASC is developed using nickel–cobalt sulfide (NiCo 2 S 4 )/polyaniline (PANI)/manganese dioxide (MnO 2 ) ternary composite on carbon fiber felt (CF) as positive and N, S‐co‐doped carbon nanofibers (CNF)/CF as negative electrode, respectively. Initially, porous δ‐MnO 2 nanoworm‐like network is decorated on CF using potentiodynamic method. Subsequently, interconnected PANI nanostructures is grown on the MnO 2 via a facile in situ chemical polymerization, followed by the electrodeposition of highly porous NiCo 2 S 4 nanowalls. Benefiting from 3D porous structure of conductive CF and redox active properties of NiCo 2 S 4 , PANI and MnO 2 , FAASC achieved a superior energy storage capacity. Later, high‐performance N, S‐co‐doped CNF/CF negative electrode is synthesized using electropolymerization of PANI nanofibers on CF, followed by the carbonization process. The assembled FAASC exhibits a wide voltage window of 2.2 V and remarkable specific capacitance of 143 F g −1 at a current density of 1 A g −1 . The cell further delivers a superb energy density of 71.6 Wh kg −1 at a power density of 492.7 W kg −1 , supreme cycle life and remarkable electrochemical stability under mechanical bending.