Nanostructured NiO plates on 3-dimensional porous nickel foam were prepared by hydrothermally treating the commercial nickel foam in an alkaline (NH4)(2)S2O8 solution followed by annealing in the air. The microstructures and electrochemical performance as well as electrochemically induced phase evolution of the nanostructured NiO electrodes were investigated. Working with a Li metal counter electrode, the hierarchically nanostructured NiO electrode presents a high reversible specific capacity of 604 mA h g(-1) at 1.25 C even after 100 cycles and excellent rate performance with a specific capacity of 320 mA h g(-1) at 8 C. TEM investigations conducted at several representative charge/discharge statuses reveal that an intermediate phase of Li2NiO2 produced during the redox conversion between metallic Ni and NiO. Therefore, the reactions of NiO electrode for Li-ion storage can be described as NiO <-> 0.5Ni + 0.5Li(2)NiO(2) <-> Ni + Li2O. (C) 2015 Elsevier Ltd. All rights reserved.