Electrochemical Stability of Thin-Film LiCoO₂ Cathodes by Aluminum-Oxide Coating

High-performance thin-film LiCoO 2 cathodes were successfully fabricated by aluminum-oxide coating. Both the galvanostatic charge−discharge experiments and the cyclic voltammograms (CVs) showed enhanced electrochemical properties in the Al 2 O 3 -coated LiCoO 2 films compared to those in the uncoated ones. The improved cycling behaviors in the coated samples are caused by the suppression of cobalt dissolution from the LiCoO 2 thin films, with the formation of an aluminum-oxide solid electrolyte residing between the LiCoO 2 cathode and liquid electrolyte. Galvanostatic intermittent titration technique (GITT) results clearly showed that the Al 2 O 3 -coated samples had higher Li diffusivities than the uncoated ones after 80 cycles. The effect of Al 2 O 3 thickness on the electrochemical properties up to 300 nm was also studied.