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 degreesC for 8 h. 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 3.24 g cm(-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.