Preparation and Characterization of LiCoO2 Thin Films by Laser Ablation Deposition

Thin films of LiCoO2 are obtained by Laser ablation from sintered LiCoO2 targets. The films were deposited on stainless steel or tantalum foil substrates so they could be used as cathodes in rechargeable thin‐film lithium batteries. The films are amorphous when deposited on unheated substrates, but crystallize readily when heated in air above 500°C. Using x‐ray diffraction, we show that the films are basically stoichiometric and have no impurity phases present. They consist partly of the normal bulk LiCoO2 phase which can be prepared by reacting Li2CO3 and CoCO3 at 850°C. However, the films also contain some of the new, low temperature LiCoO2 phase recently reported by Gummow et al. In order to understand our films better we have synthesized bulk low temperature LiCoO2 from LiNO3 and Co(NO3)2 at 400°C to measure its structure and electrochemical properties. Although the crystal structures of the high and low temperature phases do differ, they are similar enough that quantitative estimates of the amount of each phase present in our films based on diffraction data alone is difficult. On the other hand, electrochemical measurements can distinguish between the high and low temperature phases.