Electrochemical performance and surface properties of bare and TiO2-coated cathode materials in lithium-ion batteries

Electrochemical performance and spectroscopic characterizations of the decomposition products from electrolytes on native and TiO2-coated LiCoO2 and LiMn2O4 in different potential regions were investigated. The results showed that TiO2-coated materials exhibited better cyclic stability in different potential regions (i.e., 3.0-4.3 V and 3.0-4.6 V), and the decomposition of the electrolytes was suppressed on the coated materials surface. Results from FTIR and temperature-programmed-desorption mass spectroscopy (TPD-MS) showed that the decomposition of the electrolytes on the electrode surface is related to both the material measured and the oxidation potential. The causes for the formation of different oxidation products of electrolytes have been analyzed. An improved electrooxidation mechanism of the electrolytes was also proposed. It is shown that the different reactivity of cathode materials to the oxidation of electrolytes can well be related to their thermal stability in practical Li-ion batteries.