High Rate Capabilities of NiCo₂O₄-Based Hierarchical Superstructures for Rechargeable Charge Storage

Flower-shaped NiCo 2 O 4 hierarchical superstructures have been synthesized via a simple hydrothermal method with a post-annealing treatment. The single as-synthesized flower-shaped architecture is self-assembled from many nanosheets. When examined as a positive material for supercapacitors in a three-electrode configuration, the NiCo 2 O 4 electrode shows typical faradaic redox properties consistent with battery-type materials and exhibits an excellent rate performance, with a 20-fold increase in the current density from 1 to 20 A g −1 (81.7% capacity retention of that at 1 A g −1 ).