Lithium ion batteries are widely used in many portable devices; however, their power density is not sufficient for use in electric vehicles. One of the most effective methods to improve the power density is the use of very fine cathode particles. We investigated a new excess lithium method of preparing nano-sized LiCoO2 powders. To begin with, lithium acetate and cobalt acetate are mixed by the molar ratio 9, 13 or 21 to 1, uniformly. The mixture is then calcined at 600°C for 6h. Finally, obtained powders are washed with a large amount of water to remove impurity and then dried. Using this method, we obtained nano-sized spherical LiCoO2 particles with a diameter of about 25nm or needlelike LiCoO2 particles with a diameter of about 5nm and a length of about 60nm. The discharge capacity of a Li/5μm LiCoO2 cell is 51mAhg−1, but when the nano-sized LiCoO2 was used, the capacity increased to about 100mAhg−1 at the same cycling condition.