Transition metal oxides are promising candidates for lithium-ion battery electrodes, while their performances are generally limited by their poor electrical conductivity and cycling stability. In this paper, we report the growth of aligned, single-crystalline NiO nanoflake arrays directly on copper substrates by a modified hydrothermal synthesis and post-annealing. The close contact of NiO nanoflakes on a current collector (e.g. Cu) allows for efficient charge transport, and waives the need for adding ancillary conducting materials or binders. In addition, the mesopores inside the NiO nanoflakes and the spacing between the adjacent aligned nanoflakes provide efficient ion transport pathways as well as sufficient flexibility for electrode volume expansion. As proof-of-concept, anodes made of NiO nanoflakes directly grown on Cu showed a high capacity and excellent cycling stability. The capacity was retained at 720 mA h g⁻¹ over 20 cycles at a current density of 100 mA g⁻¹, almost equal to the theoretical value of NiO and much higher than the NiO products formed in the same growth solution. Even at a high discharge–charge rate of 1 A g⁻¹ (1.5 C), the NiO nanoflakes grown on Cu were capable of retaining a capacity of 500 mA h g⁻¹ over 40 cycles. Our report suggests that NiO nanoflakes may serve as a promising anode material for a high-power lithium-ion battery.