Structural, electrochemical and thermal properties of LiNi0.8-yTiyCo0.2O2 as cathode materials for lithium ion battery

Multiple substitution compounds with the formula LiNi0.8-yTiyCo0.2O2 (0 less than or equal to y less than or equal to 0.1) were synthesized by sol-gel method using citric acid as a chelating agent. The effects of titanium substitution on the structural, electrochemical and thermal properties of the cathode materials are investigated. A solid solution phase (R-3m) is observed in the range of 0 less than or equal to y less than or equal to 0.1 for the titanium-doped materials. X-ray photoelectron spectroscopy (XPS) shows that there are Ni3+, Ni2+, Co3+, Co2+ and Ti4+ five transition metal ions in titanium-doped materials. Rietveld refinement of X-ray diffraction (XRD) patterns indicates that titanium substitution changes the materials' structure with different cationic distribution. An increase of the Ni/Co amount in the 3a Li site is found with the addition of titanium amount. An improved cycling performance is observed for titanium-doped cathode materials, which is interpreted to a significant suppression of phase transitions and lattice changes during cycling. The thermal stability of titanium-doped materials is also improved, which can be attributed to its lower oxidation ability and enhanced structural stability at delithiated state. (C) 2003 Elsevier Ltd. All rights reserved.