3D in-situ hollow carbon fiber/carbon nanosheet/Fe3C@Fe3O4 by solventless one-step synthesis and its superior supercapacitor performance

•3D in-situ h-CNF/CNS/Fe3C@Fe3O4 was constructed using ferrocene and oleic acid by a solventless one-step process.•h-CNF/CNS/Fe3C@Fe3O4 exhibited higher specific capacitance of 327Fg−1 at 5mVs−1 and 210Fg−1 at 10mVs−1, and superior retention of 108% after 6000 cycles at 100mVs−1.•Carbon nanoshell comprising h-CNF and CNS well encapsulates Fe3C@Fe3O4 core materials and this sturdy structure endows high cycle stability up to 6000 cycles.