LiCoO2 is currently used as a cathode material in most commercial lithium-ion batteries. Lithium intercalation compounds such as LiNiO2 are being pursued as lower cost alternatives to LiCoO2. Although cathodes of LiNiO2 provide higher capacity at a lower cost the layered structure becomes unstable during the cell charging process as the material is delithiated. The instability of LiNiO2 in lithium-ion cells reduces the cycle life of the cell and leads to safety concerns. Ir, this paper we determine the influence of particle size and particle morphology on the thermal stability of lithiated LiNiO2. Five different particle size (P-c) cathode materials were prepared by a proprietary Westaim process and the thermal and electrochemical stability determined. Thermogravimetric analysis indicates that the thermal stability of LiNiO2 depends on P-c, not on the particle size of the agglomerate (P-a). LiNiO2 with a large P-c is more thermally stable than those with a small P-c. The LiNiO2 cathode material exhibits a reversible electrochemical capacity of about 150 mAh/g when tested in an Li/LiNiO2 cell. The LiNiO2 cathode material with a large P-c has a slightly lower reversible capacity than that with a small P-c.