Porous CuO nanosphere films have been successfully prepared through post-heat treatment of Cu-2(OH)(2)CO3 nanosphere films, which were formed on copper foil immersed in a water-in-oil (W/O) microemulsion. The electrochemical performance of the porous CuO nanosphere film as anode materials for lithium ion batteries indicates that at the current density of 0.1 C, it exhibits higher initial coulombic efficiency (70.4%) and reversible discharge capacity (799.7 mA hg(-1) after 100 cycles) than the CuO nanorod film on copper foil, which was obtained via aqueous solution oxidation reaction followed by post-heating in N-2 flow. The excellent performance can be attributed to the novel porous nanosphere structure grown on the current collecting substrate, which could not only shorten the diffusion path of lithium ion and provide appropriate contact area between electrode and electrolyte, but also increase the electrical conductivity of the electrode. More generally, the strategy based on synthesis within confined reaction media, rather than direct synthesis in bulk solution, offers a new approach to the design of micro/nanostructured transition metal oxides grown on the current collecting substrate used as anodes in lithium ion batteries with enhanced electrochemical performance. (C) 2013 Elsevier Ltd. All rights reserved.