Rapid and economical fabrications of macroporous materials are of general interest in various fields of energy storage, energy conversion, catalysis and gas sensors. In this paper, macroporous NiO/Ni powders were achieved in a flash by the direct decomposition of a metal complex, which is template-free, surfactant-free and highly effective. The metal complex was achieved by simply mixing nickel acetate, nickel nitrate, hydrazine hydrate and glycine in water. The pore size, porosity and even morphology of the porous network (three- or two-dimensional architectures) can be conveniently tuned by adjusting the composition of the complex. It is found that, the amounts of hydrazine hydrate and glycine in the reactants affected the morphology of the porous network; whilst that of nickel acetate determined the macropores. The electrochemical performance of the achieved macroporous NiO/Ni as anodes in Li-ion batteries was comparatively investigated. The 3D macroporous NiO/Ni powders exhibited better electrochemical performances than that of 2D macroporous NiO/Ni and 3D compact NiO/Ni because of its better electrical conductivity and unique porous architecture. The presence of Ni and the continuous network of 3D structures improved the electrical conductivity of electrode materials. In addition, the macroporous architectures not only favored the ingress of electrolytes but also compensated the large volume change of the active materials during the cycling.