Enhanced electrochemical performance and thermal stability of La2O3-coated LiCoO2

An enhanced electrochemical performance LiCoO2 cathode was synthesized by coating with various wt.% of La2O3 to the LiCoO2 particle surfaces by a polymeric method, followed by calcination at 923 K for 4 h in air. The surface-coated materials were characterized by XRD, TGA, SEM, TEM, BET and XPS/ESCA techniques. XRD patterns of La2O3-coated LiCoO2 revealed that the coating did not affect the crystal structure, alpha-NaFeO2, of the cathode material compared to pristine LiCoO2. TEM images showed a compact coating layer on the surface of the core material that had an average thickness of about similar to 15 nm. XPS data illustrated that the presence of two different environmental 0 1s ions corresponds to the surface-coated La2O3 and core material. The electrochemical performance of the coated materials by galvanostatic cycling studies suggest that 2.0 wt.% coated La2O3 on LiCoO2 improved cycle stability (284 cycles) by a factor of similar to 7 times over the pristine LiCoO2 cathode material and also demonstrated excellent cell cycle stability when charged at high voltages (4.4, 4.5 and 4.6 V). Impedance spectroscopy demonstrated that the enhanced performance of the coated materials is attributed to slower impedance growth during the charge-discharge processes. The DSC curve revealed that the exothermic peak corresponding to the release of oxygen at similar to 464 K was significantly smaller for the La2O3-coated cathode material and recognized its high thermal stability. (c) 2006 Elsevier Ltd. All rights reserved.