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

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 (NiCo2S4)/polyaniline (PANI)/manganese dioxide (MnO2) ternary composite on carbon fiber felt (CF) as positive and N, S-co-doped carbon nanofibers (CNF)/CF as negative electrode, respectively. Initially, porous delta-MnO2 nanoworm-like network is decorated on CF using potentiodynamic method. Subsequently, interconnected PANI nanostructures is grown on the MnO2 via a facile in situ chemical polymerization, followed by the electrodeposition of highly porous NiCo2S4 nanowalls. Benefiting from 3D porous structure of conductive CF and redox active properties of NiCo2S4, PANI and MnO2, 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.