LiCoO2 cathode powders with a grain size of 1-1.5 mum were synthesized by a mechanochemical process. The Li-Co precursor was prepared by a freeze drying method using a Li and Co acetate as starting raw materials. The surface was modified by lapping the precursor using K2SO4 in a simple ballmill. After the surface modification, the Li-Co precursor was heated at 800degreesC to form a high-temperature polymorph. The K2SO4 coat on the Li-Co precursor prevented the Li-Co precursors from contacting one another, due to the high decomposition temperature of K2SO4 above 1000degreesC and constrains grain growth. Because of this, the modified Li-Co precursor is converted to very small crystalline LiCoO2 particles by phase transformation. The as-synthesized LiCoO2 powder had well-developed facets and a very uniform grain size distribution. A small capacity fade for high discharge rate was observed in the as-synthesized powder, which can be attributed to the diffusion of Li ions at the grain boundary. Thus, it is possible not only to synthesis LiCoO2 powder to a desired grain size but also to control the grain size distribution using this method. These results indicated that the synthesis of a high-temperature polymorph of LiCoO2 with a small grain size is possible by constraining growth during the heat-treatment. The LiCoO2 powder synthesized here represents a very good candidate for use in fabricating not only of high power bulk batteries but high power slim batteries as well, when a thin and thick film process is used. (C) 2004 The Electrochemical Society.