Studies of LiCoOx thin film cathodes produced by r.f. sputtering

Thin films of LiCoOx were deposited by r.f. sputtering, from a LiCoO2 target and in an O2/Ar atmosphere. The structural properties were studied by XRD and IR, the morphology by AFM and the electrochemical properties by cyclic voltammetry and galvanostatic charge/discharge techniques in 1 M LiClO4/PC+EC electrolyte. As-grown films were amorphous and presented compact grain morphology. Annealing promotes a melt of the film at 300°C, followed by crystallisation at higher temperatures. The IR and XRD spectrum of films annealed in air showed the same structural reordering above 300°C. The crystalline film has been identified as a mixed LiCoO2+Li1.47Co3O4 phase. The open circuit potential for both films is 3.45 V. The films can be cycled till not, vert, similar4.2 V, but the crystalline structure presents irreversible phase changes, which limits the cyclability of the material. The films are interesting potential materials to be used at cathodes in lithium batteries.