Assembling complex nanostructures on functional substrates such as electrodes promises new multi-functional interfaces with synergetic properties capable of integration into larger-scale devices. Here, we report a microemulsion-mediated process for the preparation of CuO/Cu electrodes comprising a surface layer of a densely packed array of unusual cog-shaped CuO microparticles with hierarchical nanofilament-based superstructure and enhanced electrochemical performance in lithium-ion batteries. The CuO particles are produced by thermolysis of Cu(OH)(2) micro-cog precursors that spontaneously assemble on the copper substrate when the metal foil is treated with a reactive oil-based microemulsion containing nanometer-scale aqueous droplets. The formation of the hierarchical superstructure improves the coulombic efficiency, specific capacity, and cycling performance compared with anodes based on CuO nanorods or polymer-blended commercial CuO/C black powders, and the values for the initial discharge capacity (1052 mA h g(-1)) and reversible capacity (810 m A h g(-1)) are higher than most copper oxide materials used in lithium-ion batteries. The results indicate that a fabrication strategy based on self-assembly within confined reaction media, rather than direct synthesis in bulk solution, offers a new approach to the design of electrode surface structures for potential development in a wide range of materials applications.