XPS study on Al2O3- and AlPO4-coated LiCoO2 cathode material for high-capacity li ion batteries

The impact of aluminum oxide coatings on LiCoO2 materials for commercial lithium ion batteries has been investigated by X-ray photoelectron spectroscopy (XPS) . A low binding energy component in the Al 2p core peak spectra was observed and attributed to the formation of a LiAlxCo(1-x)O2 solid solution interphase for both Al2O3- and AlPO4- coated LiCoO2. The surface chemistry of pristine and Al2O3-coated LiCoO2 cathodes and graphite anodes have been investigated after cycling up to 4.2 V or 4.4 V cutoff voltage and after various levels of capacity fade. The Al2O3 coating enhances the capacity retention at both 4.2 V and 4.4 V cutoff voltages. XPS analyses provided evidence of the inhibition of cobalt dissolution from the LiCoO2 positive electrode by the aluminum coatings. Moreover, the Al2O3 coating lowers the kinetics of degradation of electrolyte species, especially the LiPF6 salt. (c) 2007 The Electrochemical Society.