Characterization of sprayed and sputter deposited LiCoO2 thin films for rechargeable microbatteries

Thin films of LiCoO2 have been prepared by both spray pyrolysis and r.f. sputtering. Structural properties of the films have been investigated by X-ray powder diffraction and scanning electron microscopy. The LiCoO2 hexagonal high-temperature phase was obtained on the samples after post-deposition annealing treatments at 600 degrees C in air. Films as thin as 75 nm have been deposited on large aluminium and aluminium/ gold substrates. Sputter deposition improved the density and homogeneity of thin films compared with the spray pyrolysis method. Cells with sprayed and sputtered LiCoO2 compounds versus lithium using LiClO4 in propylene carbonate as the liquid electrolyte have been tested, the importance of annealing the thin films before cycling discussed, and the importance of the substrate in the cycling behaviour is evidenced. The cyclic voltammograms demonstrate that the LiCoO2 cathodes prepared by both methods are electrochemically active, showing promising cycling behaviour.