A New Look at Lithium Cobalt Oxide in a Broad Voltage Range for Lithium-Ion Batteries

The electrochemical behaviors and lithium-storage mechanism of LiCoO2, in a broad voltage window (1.0-4.3 V) are Studied by charge-discharge cycling, XRD, XPS, Raman, and HRTEM. It is found that the reduction mechanism of LiCoO, with lithium is associated with the irreversible formation of metastable phase Li1+xCoII O-III(2-y) and then the final products of Li2O and Co metal. During the charging process, the Li2O/Co mixture can be oxidized into CoO, and then the LiO/CoO mixture can result in the formation of Co3O4 in the higher-voltage region. LixCoOy is the final product when the active material is charged to 4.3 V. During the subsequent cycles, the lithium uptake/release reactions ire related to the reversible conversion of Co <-> CoO <-> Co3O4 <-> LixCoOy.