In-situ partial reduction‑sulfurized Fe3O4@FeS based on pickling iron red as a versatile electrode for high-performance lithium ion batteries and supercapacitor devices

In this study, Fe3O4@FeS composites have been successfully synthesized by a facile and low-cost solid-phase reaction and in-situ growth process. This method provides a new idea for the comprehensive utilization of pickled iron oxide red and saves the cost of FeS preparation. In addition, the refining results of X-ray diffraction (XRD) and Mössbauer spectroscopy test results show that the composite structure of FeS coated Fe3O4 is successfully synthesized. As an electrode for lithium ion batteries and supercapacitors, the conductivity and electrochemical property of the Fe3O4@FeS composites electrode is far beyond that of the pure FeS. The unique structure markedly improves the electrochemical property and conductivity of FeS, indicating that the synergistic effect between FeS and Fe3O4 plays a vital role during discharge process. In particular, the kinetic analysis shows that the pseudo capacitance contribution rate of the electrode material is as high as 98.6%. An all-solid-state hybrid supercapacitor fabricated with Fe3O4@FeS as a positive delivers an ultrahigh specific energy of 64.6 W h kg−1 at power density of 800 W kg−1 and still retains 21.8 W h kg−1 even at 8000 W kg−1. The electrochemical properties show that the prepared electrode materials have excellent commercial application potential.