Ball mill assisted synthesis of cobalt–iron sulfide/N-doped carbon for high performance asymmetric supercapacitors

Abstract

Cobalt–iron sulfides supported on N-doped carbon were synthesized as energy storage material using ball milling followed by carbonization. As-synthesized materials were structurally analyzed by X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, scanning electron microscopy, and high-resolution transmission electron microscopy. Furthermore, cobalt–iron sulfides supported on N-doped carbon were coated on Ni foam, and their electrochemical performance was tested in a 3-M KOH electrolyte. The as-fabricated Co–Fe–S-2 electrode registered a specific capacitance of 1252 F g−1 at 1 A g−1 and also showed capacitance retention of 66.4% at 20 A g−1. In addition, asymmetric supercapacitors (ASC) were fabricated using the as-synthesized electrode materials and it had a voltage window of 0–1.6 V. Among them, the activated carbon (AC)//Co–Fe–S-2 ASC device showed maximum specific capacitance of 169.3 F g−1 at 1 A g−1, and it registered maximum energy density of 59.6 Wh kg−1 at power density of 0.796 kW kg−1. The AC//Co–Fe–S-2 device delivered a rate capability of 55.6% at 30 A g−1, and it reveals a capacitance retention of 76.3% over 5000 cycles. Herein we also found that ball-milling-assisted synthesis of Co–Fe–S-2 electrode material is a promising candidate for high-performance ASCs.