[en] A simple process is reported of the large-scale synthesis of microspherical mixed phase α- and β-Ni(OH)_2 nanofibers produced by precipitation from aqueous NiCl_2–NH_4OH. These microspheres, with diameters of 20–50 μm, are composed of three-dimensional, nanoporous nanofibers, oriented along the radial direction. The nanofibers have lengths of 300–1000 nm, diameters of 30–50 nm and a specific surface area of 286.4 m"2 g"−"1. The effects of temperature and concentration on the morphology of the products were studied systematically, and the nanofiber growth mechanism was investigated. It was found that the nanostructure of Ni(OH)_2 could be changed from microspheres to nanoflakes, to nanofibers and nanoparticles, as the NiCl_2 concentration is increased from 2 to 8 M, and for NH_4OH concentrations from 10 to 14 M. The as-synthesized nanofibers exhibit excellent charge–discharge performance and the highest yet capacitance of 1271 F g"−"1 for electrochemical supercapacitors, which is much higher than β-Ni(OH)_2 nanoplates (797 F g"−"1) and commercial Ni(OH)_2 powder (529.4 F g"−"1) at 1 A g"−"1 current density. The results indicate that as-synthesized hierarchical nanofibers, composed of mixed α- and β-Ni(OH)_2 phases, are an excellent candidate for energy storage applications. The large-scale commercialization of our laboratory-produced nanofibers is also discussed. (paper)