A series of cathode materials for lithium ion batteries with the formula LiNi0.8-xCo0.2CexO2 (0 <= x <= 0.03) were synthesized by sol-gel method using citric acid as a chelating agent. The effects of cerium substitution on the structural, electrochemical and thermal properties of the cathode materials are investigated through X-ray diffraction (XRD), charge-discharge cycling, cyclic voltammogram (CV), electrochemical impedance spectroscopy (EIS) experiments and differential scanning callorimetry (DSC). Results show that the Ce substitution made the layered structure of materials more regular and less cation-ion mixing. An effective improved cycling performance is observed for cerium-doped cathode materials, which is interpreted to a significant suppression of phase transitions and charge-transfer impedance increasing during cycling. The thermal stability of cerium-doped materials is also improved, which can be attributed to its lower oxidation ability and enhanced structural stability at delithiated state. (c) 2006 Published by Elsevier B.V.