Ball-like LiMn0.4Ni0.4Co0.2O2 particles composed of flakes were synthesized by a simplified co-precipitation method followed by a solid-state reaction at temperatures of 600-900 degrees C. The relationship between the flake thickness and the electrochemical performance of the layered oxides was investigated in this work. The layered oxide with a flake thickness of 80-100 nm synthesized at 800 degrees C has the best electrochemical performance among these cathode materials, especially the rate capability. An initial discharge capacity of 160 mAh g(-1) was obtained at 5 C (1400 mA g(-1)) in the voltage range of 2.5-4.5 V, and the capacity retention was 80% after 50 cycles. The excellent rate capability is attributed to the well formed structure, short diffusion distance and good crystallinity. In addition, a detailed study of diffusion coefficient of Li+ (DLi+) was carried out to further understand this material. The value of DLi+ calculated is in the range of 10(-11) to 10(-12) cm(2) s(-1). (C) 2012 Elsevier Ltd. All rights reserved.