Morphologically confined hybridization of tiny CoNi2S4 nanosheets into S, P co-doped graphene leading to enhanced pseudocapacitance and rate capability

Abstract The transition metal hydroxides/sulfides have been regarded as novel high-efficient electrode materials due to its superior Faradic activity. However, the aggregation problem and poor rate performance severely hinder the practical application in supercapacitors. Herein, morphologically confined hybridization of tiny CoNi2S4 nanosheets into S, P co-doped graphene (DGNCS) is designed and fabricated from NiCo-OH precursor (NCO) nanowires via a mild multi-step hydrothermal method and sulfofication. The S, P co-doped graphene (DG) serves as the conductive pathway and skeleton support and provides abundant coordination atoms to prevent the aggregation and improve the structural stability. The CoNi2S4 nanosheets serves as the main active components and provides abundant active sites to enhance the electrochemical performance. Owing to the synergistic effect of each components, the as-prepared DGNCS electrode delivers a specific capacitance of 1136.5 F g−1 (126.28 mAh g−1) at 2 A g−1 and a satisfactory capacitance retention of 70.1% after 5000 cycles at 15 A g−1. In addition, the rate performance of DGNCS (38.58%) increased by 2.44 times compared with the pure NCS (CoNi2S4). Furthermore, the fabricated asymmetric supercapacitor (ASC) device assembled with active graphene and the as-obtained DGNCS achieves a maximum energy density of 25.62 Wh kg−1 and an outstanding power density of 8000 W kg−1. Moreover, the ASC device shows an excellent cycling stability of 86.49% capacitance retention after 5000 cycling at 5 A g−1. Outstanding electrochemical performance confirms the effectiveness of the fabricating strategy, providing a new pathway for further design of a novel composite electrode for next generation energy storage devices.