Controllable preparation of core-shell Co3O4@CoNiS nanowires for ultra-long life asymmetric supercapacitors

Abstract Tricobalt tetroxide (Co3O4) with high theoretical capacity has been considered as a promising material for supercapacitors. However, the poor electrical conductivity and poor capacity retention hinder its further larger-scale application. Besides, a series of metal sulfides shows good thermal stability, mechanical stability and electrical conductivity. Here, hierarchical core-shell nanostructure is successfully synthesized by coating the Co3O4 nanowires with highly conductive CoNiS (Co3O4@CoNiS) by a facile two-step method of hydrothermal treatment and succeeding electrodeposition. And the core-shell structure presents high electrical conductivity, discharge capacity and good cycle life. The as-prepared Co3O4@CoNiS exhibited a high specific capacity of 1153.75 C g−1, which is 1.97 times as much as that of Co3O4. Furthermore, an asymmetric supercapacitor (ASC) was assembled by using the N/O co-doped porous carbon (NOPC) as negative electrode and the as-prepared Co3O4@CoNiS as positive electrode, which showed a high energy density of 46.95 Wh kg−1 at the power density of 400 W kg−1 and an ultra-stable capacity retention with 95.6% for 20,000 cycles. The cyclic stability of similar work is lower than that of our work, which provides a reference for the preparation of electrode materials with long-term cyclic stability.