Self-assembled Ni 3 S 2 //CoNi 2 S 4 nanoarrays for ultra high-performance supercapacitor

In this study, Ni3S2-nanorod and CoNi2S4-microflower structures have been prepared using a simple one-step hydrothermal method. The complete absence of an additive polymeric binder enabled the electrode to obtain structural purity and excellent electrochemical activity. The formation of the nanorod and micro flowers (µflowers) was clearly visualized by the surface microstructural study. Ni3S2-nanorod and CoNi2S4-µflower electrodes show a significantly higher specific capacitance of 982.9 F g−1 and 2098.95 F g−1, respectively, with outstanding electrochemical cyclic stability performance. The CoNi2S4-µflower electrode can achieve an energy density of 82.98 Wh kg−1 with a power density of 9.63 kW kg−1. In addition, a 91% capacitive retention remains after 2000 cycles at a scan rate of 100 mV s−1. The designed hybrid asymmetric supercapacitor, based on Ni3S2-nanorod//CoNi2S4-µflower electrodes, exhibits a specific capacitance of 54.92 F g−1 at a scan rate of 5 mV s−1. The assembled asymmetric supercapacitor has an energy density of 6.6 Wh kg−1 while delivering a power density of 820 W kg−1. The capacitive retention of the initial capacitance remains desirable at 89.13% after 5000 CV cycles at a scan rate of 100 mV s−1. The present work manifests a vision for the fabrication of self-assembled, binder-free electrodes for high-performance hybrid supercapacitor application.