Porous NiCo2O4 spheres tuned through carbon quantum dots utilised as advanced materials for an asymmetric supercapacitor
Carbon quantum dots (CQDs) tuned porous NiCo2O4 sphere composites are prepared for the first time via a reflux synthesis route followed by a post annealing treatment. Benefiting from the advantages of the unique porous structure with a large specific surface area, high mesoporosity and superior electronic conductivity, the as-obtained CQDs/NiCo2O4 composite electrode exhibits high specific capacitance (856 F g−1 at 1 A g−1), excellent rate capability (83.9%, 72.5% and 60.8% capacity retention rate at 20, 50 and 100 A g−1, respectively) and exceptional cycling stability (98.75% of the initial capacity retention over 10 000 cycles at 5 A g−1). Furthermore, the assembled AC//CQDs/NiCo2O4 asymmetric supercapacitor manifests a high energy density (27.8 W h kg−1) at a power density of 128 W kg−1 or a high power density (10.24 kW kg−1) at the reasonable energy density of 13.1 W h kg−1 and remarkable cycling stability (101.9% of the initial capacity retention over 5000 cycles at 3 A g−1). The results above suggest a great potential of the porous CQDs/NiCo2O4 composites in the development of high-performance electrochemical energy storage devices for practical applications.