LiNi1-xCoxO2 is being considered for use as a cathode material in commercial lithium-ion batteries because of its higher capacity and lower material cost than its end member LiCoO2. On the other hand, LiNi1-xCoxO2 has better thermal stability than its other end member LiNiO2. In this paper we examine the influence of particle size and particle morphology on the electrochemical behavior of LiNi1-xCoxO2 and the dependence of the irreversible capacity on Co content, temperature, and particle size. Coin cell performance at room temperature and at 40 degrees C indicates that LiNi1-xCoxO2 with a large crystal particle size (P-c) has a low capacity fade rate. The irreversible capacity is reduced at high temperature. By optimizing particle size and cobalt content in LiNi1-xCoxO2, it is possible to achieve cycle performance comparable with LiCoO2 at room temperature and at 40 degrees C, and have a reversible capacity (between 150 and 200 mAh/g) substantially high er than LiCoO4 (140 mAh/g). LiNi1-xCoxO2 (0.1 < x < 0.3) tested at C/1 discharge and at 40 degrees C also shows a low capacity fade rate comparable to that of LiCoO2 material.