Effects of oxygen pressure on LiCoO2 thin film cathodes and their electrochemical properties grown by pulsed laser deposition

LiCoO2 thin films have been deposited by pulsed laser deposition (PLD) at 600 degrees C and various pressures of oxygen. At 300 mTorr of oxygen, (003) oriented and well crystallized LiCoO2 thin films with a little large size of grains were grown. However, randomly oriented LiCoO2 films were obtained at 50 mTorr of oxygen. In cyclic voltammetry (CV) scans, the (003) oriented film cathode showed only one pair of main anodic and cathodic peaks at low potentials with a narrow peak separation while the randomly oriented film had two other pairs of minor peaks at high potentials besides a pair of major peaks at low potentials. The (003) oriented film had 40.2 mu Ah/cm(2) mu m of discharge capacity, whereas the randomly oriented LiCoO2 film achieved a maximum discharge capacity of 60.1 mu Ah/cm(2) mu m with the same current density of 50 mu A/cm(2). Moreover, the cycling stability and coulombic efficiency of the randomly oriented film were also better than those of the (003) oriented film. (c) 2006 Elsevier B.V. All rights reserved.