Characterization of a LiCoO₂ thin film cathode grown by pulsed laser deposition

Abstract

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 Li_0.5CoO₂, 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.

Acknowledgements

The authors thank Ni Zhenhua and Professor Shen Zexiang for their help in measuring Raman spectra. This work was supported by the National University of Singapore under projects R265-000-133-112 and R265-000-162-112.