The lithium secondary batteries with high power density need the electrode materials with both high specific capacity and high tap-density. LiNi0.8Co0.2O2 cathode material is a very promising candidate to replace the commercialized LiCoO2 for lithium secondary batteries. Spherical Ni0.8Co0.2(OH)2 powders were prepared via a “controlled crystallization” method using NiSO4, CoSO4, NaOH and NH3·H2O. Spherical LiNi0.8Co0.2O2 powders with order layered structure were easily synthesized by firing LiOH·H2O and the spherical Ni0.8Co0.2(OH)2 in oxygen at 750°C for 8h. The relation among the “controlled crystallization” conditions and the Ni0.8Co0.2(OH)2 and LiNi0.8Co0.2O2 powders’ structure, particle morphology, particle size, particle size distribution, and tap-density was investigated. It is shown that with the suitable “controlled crystallization” conditions, the tap-density of the spherical LiNi0.8Co0.2O2 powders can be improved as high as 3.24gcm−3, which is remarkably higher than the non-spherical LiNi0.8Co0.2O2 powders available as commercial cathode materials. The cathode materials also show high reversible specific capacity and long cycling life. The high-density spherical LiNi0.8Co0.2O2 cathode materials can greatly improve the power density of the lithium secondary batteries.