Characterization of a LiCoO2thin film cathode grown by pulsed laser deposition

A highly (003)-oriented pure LiCoO2 thin film cathode, without Co3O4 impurities, was grown on a stainless steel substrate by pulsed laser deposition and characterized by electrochemical testing, scanning electron microscopy (SEM), ex situ X-ray diffraction (XRD), Raman and X-ray photoelectron spectroscopy (XPS). The initial reversible discharge capacity of the LiCoO2 thin film cathode reached 52.5 μAh/cm2µm and capacity loss was about 0.18% per cycle at a current density of 12.74 μA/cm2. The chemical diffusion coefficient of the Li+ ion was estimated to be about 4.7 × 10−11 cm2/s from cyclic voltammetric (CV) scans. Ex situ XRD revealed that the spacing of crystalline planes expanded about 0.09 Å when charged to 4.2 V, corresponding to Li0.5CoO2, lower than the value for composite powder LiCoO2 electrodes. XPS results showed that the number of low-coordinated oxygen ions increased relative to the removal of Li+ ions.