Growth and microstructural features of laser ablated LiCoO 2 thin films

Abstract

Thin films of LiCoO 2 were prepared by pulsed laser deposition technique and the properties were studied in relation to the deposition parameters. The films deposited from a sintered composite target (LiCoO 2+Li 2O) in an oxygen partial pressure of 100 mTorr and at a substrate temperature of 300 °C exhibited preferred c-axis (0 0 3) orientation perpendicular to the substrate surface. The AFM data demonstrated that the films are composed of uniform distribution of fine grains with an average grain size of 80 nm. The grain size increased with an increase in substrate temperature. The (0 0 3) orientation decreased with increase in (1 0 4) orientation for the films deposited at higher substrate temperatures (>500 °C) indicating that the films’ growth is parallel to the substrate surface. The composition of the experimental films was analyzed using X-ray photoelectron spectroscopy (XPS). The binding energy peaks of Co(2p 3/2) and Co(2p 1/2) are, respectively, observed at 779.3 and 794.4 eV, which can be attributed to the Co 3+ bonding state of LiCoO 2. The electrochemical measurements were carried out on Li//LiCoO 2 cells with a lithium metal foil as anode and LiCoO 2 film as cathode of 1.5 cm 2 active area using a Teflon home-made cell hardware. The Li//LiCoO 2 cells were tested in the potential range 2.6–4.2 V. Specific capacity as high as 205 mC/cm 2 μm was measured for the film grown at 700 °C. The growth of LiCoO 2 films were studied in relation to the deposition parameters for their effective utilization as cathode materials in solid-state microbattery application.