Investigations on sputter deposited LicoO₂ thin films from powder target

LiCoO₂ thin films used as cathode layers in thin-film solid-state batteries have been deposited from LiCoO₂ powder target using radio frequency (rf) magnetron sputtering in a cost effective approach in terms of material consumption and processing time. Xray diffraction (XRD) studies of the films after post deposition annealing treatment revealed (104) orientation, which is the characteristic of rf sputtered LiCoO₂ films. Raman spectroscopy was used to identify the different modes of vibration of atoms in the film. The surface morphology and cross-section of the samples were characterized using field emission scanning electron microscopy (SEM). The chemical analysis of LiCoO₂ thin films was examinedby X-ray photoelectron spectroscopy (XPS) showed atomic ratio of Li/Co as 0.9 which is close to the ideal value 1. Electrochemical characterization such as charge -discharge andcyclic voltammetry were conducted for LiCoO₂ films deposited on platinized silicon substrates in the potential range 3.0 to 4.2 V vs Li/Li⁺. The maximum discharge capacity of 64 μAh.μm^-1. cm^-2 and 52 μAh. μm^-1.cm^-2 were achieved when discharged at a current of 5 μAand 50 μA for the first discharge cycle respectively. Moreover the electrochemical investigations of LiCoO₂ thin films on flexible copper substrates also investigated and achieved an initial discharge capacity of 83 mAh/g. The possible reasons for degradation in the electrochemical properties have been discussed. The present work indicates suitability of sputtering from powder targets for thin film battery fabrication.