LiNi2/3Mn1/3O2 was synthesized from LiOH center dot H2O and Ni2/3Mn1/3(OH)(2) mixed hydroxide. Four different coprecipitation routes were used to prepare the Ni2/3Mn1/3(OH)(2) precursor beginning with divalent metal nitrates or metal sulfates. When ammonia was added during the coprecipitation under anaerobic conditions, spherical and dense particles of Ni2/3Mn1/3(OH)(2) were prepared. The impact of various coprecipitation methods on the subsequent properties of LiNi2/3Mn1/3O2 was studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), and electrochemical tests. Spherical and dense particles of LiNi2/3Mn1/3O2 showed an excellent charge-discharge cycle life at 4.6 V. The impact of heating temperature and time on the properties of LiNi2/3Mn1/3O2 was also studied by XRD, SEM, and electrochemical tests and suggested that the heating temperature plays a significant role in determining the electrochemical performance of LiNi2/3Mn1/3O2. Accelerating rate calorimetry results suggest that LiNi2/3Mn1/3O2 is less thermally stable than Li[Ni1/3Mn1/3Co1/3]O-2.