LiCo 1 - x Al x O 2 (0=<x=<0.3, R3m) powders by the emulsion drying method and their microstructure studies were carried out in order to understand Al-doping effect on the electrochemical properties. Through X-ray diffraction experiment, we confirmed that Co was well substituted by Al while maintaining the α-NaFeO 2 layer structure type. The substitution of Al was effective on suppressing cobalt dissolution at 4.5 V versus Li/Li + and on diminishing changes in a- and c-axes during lithium intercalation. For x=0.1, the open-circuit voltage was slightly higher than that of undoped LiCoO 2 . Chemical diffusion coefficient of lithium in LiCo 1 - x Al x O 2 was higher than that of LiCoO 2 because of a smaller variation in the longer c-axis.