A hollow Co9S8 rod–acidified CNT–NiCoLDH composite providing excellent electrochemical performance in asymmetric supercapacitors

Abstract

Co₉S₈ and transition metal hydroxides are both potential pseudo-capacitance electrode materials for supercapacitors. Co₉S₈ has a large specific capacitance and electrochemical activity, and transition metal hydroxides have the advantages of high capacitance and redox activity due to their multiple valence metals and open layered structure. In this study, Co₉S₈ and NiCoLDH are used to form a Co₉S₈–aCNT–NiCoLDH composite electrode material by twining acidified carbon nanotubes (aCNTs) around hollow Co₉S₈ rods and then compounding nickel cobalt hydroxide (NiCoLDH) on the outside. aCNTs provide more electronic channels, which bring more active electrochemical reactions and absorb the volume expansion of Co₉S₈. The hollow Co₉S₈ rods and flower-like NiCoLDH structures ensure that the electrode has a highly open structure, which increases the contact area with the electrolyte and is beneficial for ion transport. The outer NiCoLDH can also reduce the volume expansion of Co₉S₈. These advantages ensure the high specific capacitance and rate performance of the Co₉S₈–aCNT–NiCoLDH electrode material. Co₉S₈–aCNT–NiCoLDH was used as the positive material to fabricate asymmetric supercapacitors with attractive energy density and power density, which further proved its excellent electrochemical performance.