Layered Li(Li0.2Ni0.15+0.5zCo0.10Mn0.55-0.5z)O2-zFz cathode materials for Li-ion secondary batteries

Electrochemical properties of layered Li(Li0.2Ni0.15+0.5zCo0.10Mn0.55-0.5zO2-zFz (0 <= z <= 0.10), which was synthesized by a sol-gel method, were investigated by galvanostatic cycling in the voltage range of 2.0-4.6 V at room temperature as well as at 55 degrees C. The initial discharge capacity slightly decreased with the increase in the content of fluorine dopant. However, cycling performance was greatly improved and cell impedance was significantly reduced by the fluorine doping. Capacity retention after 40 cycles at room temperature and the area specific impedance were 79% and 150 Omega cm(2) for z = 0, respectively, and 103% and 65 Omega cm(2) for z = 0.05, respectively. The Li(Li0.2Ni0.175Co0.10Mn0.525)O1.95F0.05 material charged to 4.6V also exhibited excellent thermal behavior due to the stability of the fully charged material. (c) 2005 Elsevier B.V. All rights reserved.