Preparation of c-axis oriented thin films of LiCoO2 by pulsed laser deposition and their electrochemical properties

Thin films of LiCoO2 with a preferred c-axis orientation were prepared by pulsed laser deposition. Thin films deposited for 1-2 h had a preferred c-axis orientation, but films deposited for 3h and longer lost the preferred orientation. The textures of these films were investigated in detail by transmission electron microscopy and selected area electron diffraction. The electrochemical properties of these films were compared by cyclic voltammetry and alternating current impedance spectroscopy. In the cyclic voltammograms of the c-axis oriented films, the anodic and cathodic peaks corresponding to the first-order phase transition at around 3.9 V were sharp and their peak separation was small due to their thin and uniform texture. However, their smooth surface and texture of the aligned (0 0 3) planes gave a larger charge-transfer resistance and a smaller apparent diffusion coefficient in the direction normal to the substrate, respectively, which resulted in poor utilizations (similar to 50%) of the active material. The reactivity in the single-phase region at potentials more positive than 4.0 V was lower than that of randomly oriented films. (C) 2001 Elsevier Science B.V. All rights reserved.