In this study we report the effects of the Ni content on the electrochemical properties and the structural and thermal stabilities of Li[Ni x Co y Mn z ]O2 (x = 1/3, 0.5, 0.6, 0.7, 0.8 and 0.85) synthesized via a coprecipitation method. The electrochemical and thermal properties of Li[Ni x Co y Mn z ]O2 are strongly dependent on its composition. An increase of the Ni content results in an increase of specific discharge capacity and total residual lithium content but the corresponding capacity retention and safety characteristics gradually decreased. The structural stability is related to the thermal and electrochemical stabilities, as confirmed by X-ray diffraction, thermal gravimetric analysis, and differential scanning calorimetry. Developing an ideal cathode material with both high capacity and safety will be a challenging task that requires precise control of microstructure and physico-chemical properties of the electrode.