All-solid-state asymmetric supercapacitor with MWCNT-based hollow NiCo₂O₄ positive electrode and porous Cu₂WS₄ negative electrode

To develop a high-performance supercapacitor, synergy between the positive and negative electrodes is essential. On the positive side, saturation is achieved in exploring novel materials, whereas on the negative side, there are extremely limited options. In this study, we propose a novel combination of hollow metal oxide positive and porous metal sulfide negative electrodes incorporated with MWCNTs to achieve advanced supercapacitors. We have rationally designed hierarchical hollow spheres of NiCo₂O₄, as positive electrodes, by carefully tuning the reaction and annealing parameters. We propose a novel material, i.e., porous Cu₂WS₄, which has never, to the best of our knowledge, been explored as negative electrodes for supercapacitors. Even though both the materials showed reasonably good electrochemical performance, to further improve their output, they were clubbed with MWCNTs to form composites. The strategy of incorporating MWCNTs worked well and the electrochemical properties were significantly improved. Both the composite electrodes exhibited an ultrahigh specific capacitance of 2240 and 1420 F g⁻¹, respectively. The fabricated solid-state asymmetric supercapacitor exhibited remarkably high specific capacity and energy density 116 mAh g⁻¹ and 87 Wh kg⁻¹, respectively, at 1 A g⁻¹. The device was also perfect in terms of power, coulombic efficiency and cycling stability for >10,000 cycles with ~88% capacity retention. The observed results pave a modern way of optimizing electrode materials and combining them to achieve high-performance hybrid supercapacitors for large scale integrated energy-storage systems.