Spinel Nickel Cobaltite Mesostructures Assembled from Ultrathin Nanosheets for High-Performance Electrochemical Energy Storage

Transition metal oxides (TMOs) are promising electrode materials for advanced electrochemical energy storage (EES) due to their high theoretical capacities, but they usually exhibit quite poor practical performance. There is a pressing need to boost their EES performance by electrode engineering directed with a well-defined structure-performance relationship. Herein, we report an efficient approach to improve the specific capacitance and high-rate capability of spinet nickel cobaltite by constructing three-dimensional (3D) hierarchical porous mesostructures. The optimal Ni1.4Co1.6O4 mesostructures assembled from ultrathin nanosheets exhibit high capacitance (2282 F g(-1) at 1 A g(-1)), excellent high-rate capability (1234 F CI at 50 A g(-1)) and good cycling performance, which are significantly superior to the Co3O4 mesostructure counterparts, Ni1.4Co1.6O4 mesostructures assembled from nanowires, and randomly packed Ni1.4Co1.6O4 nanosheets. The excellent performance is attributed to the stable hierarchical porous architecture which enables a large electroactive area and synergistically enhanced electrolyte access, solid-state ion diffusion, and electron transfer. This tactic of constructing a 3D mesostructured electrode with enhanced charge transport can be generalized to other TMOs for improving their EES performances.