Free-standing quasi-single-crystalline NiO nanowall array is successfully fabricated via a simple hydrothermal synthesis method. The as-prepared NiO film exhibits a highly porous nanowall structure composed of many interconnected nanoflakes with thicknesses of similar to 20 nm. The NiO nanowalls arrange vertically to the substrate resulting in the formation of extended porous net-like structure with pores of 30-300 nm. As anode material for lithium ion batteries, the quasi-single-crystalline NiO nanowall array exhibits pretty good electrochemical performances with high capacity, weaker polarization, higher coulombic efficiency and better cycling performance as compared to the dense polycrystalline NiO film. The quasi-single-crystalline NiO nanowall array presents an initial coulombic efficiency of 76% and good cycling life with a capacity of 564 mAh g(-1) at 0.5 A g(-1), after 50 cycles, higher than that of the dense polycrystalline NiO film (358 mAh g(-1)). The enhanced performance is due to the unique nanowall array structure providing faster ion/electron transport and better morphological stability. (c) 2012 Elsevier Ltd. All rights reserved.