Embedding NiS nanoflakes in electrospun carbon fibers containing NiS nanoparticles for hybrid supercapacitors

Carbon fibers consistently suffer from low specific capacitance due to underutilized structure, severely hindering their application in high-performance supercapacitors. In this work, a novel and scalable “inner-outer synergistic strategy” is developed for superior electrode materials via embedding NiS nanoflakes in electrospun carbon fibers containing NiS nanoparticles (NiSNF/[email protected]NP). Uniformly sized NiS nanoparticles are encapsulated in the inner region of the carbon fibers as redox active agent, which impart additional Faraday capacitance to the electrode while efficiently avoiding the aggregation of the nanoparticles. Simultaneously, the evenly distributed NiS nanoflakes firmly immobilized on the outer surface of the carbon fibers by the impregnating-sulfurization procedure significantly expand the accessible area of ions and alleviate the volume expansion by preventing stacking. Profiting from the felicitous designed architecture, the NiSNF/[email protected]NP-3 electrode delivers a reversible specific capacitance of 1691.1F g−1 at 1 A g−1 and remarkable coulombic efficiency of 98.5 %. Furthermore, the hybrid supercapacitor demonstrates a maximum energy density of 31.2 Wh kg−1 and a power density of 4004.3 W kg−1 along with impressive cycling durability of 87.8 % retention for up to 5000 cycles. This demonstrated “inner-outer simultaneous exploitation” engineering provides an appealing and instructive insight for enhanced electrochemical performance of fibrous materials, and can be extended to a variety of energy material systems.