Substrate effect on the microstructure and electrochemical properties of LiCoO2 thin films grown by PLD

LiCoO2 thin films have been grown by pulsed laser deposition on stainless steel (SS) and SiO2/Si (SOS) substrates. The structure properties of LiCoO2 thin films on both substrates were investigated. The electrochemical properties of LiCoO2 thin films on both substrates were investigated by cyclic voltammetry (CV) and charge–discharge against a lithium anode. Thin films on SS substrates showed rough surfaces and random orientation, while those on SOS substrates showed relatively smooth surfaces and preferred (0 0 3) out-of-plane orientation. Cyclic voltammograms (CVs) of randomly oriented thin films on SS substrates showed wide peaks at about 3.9 V which correspond to the first order phase transition, while CVs of preferred (0 0 3)-oriented thin films on SOS substrates showed sharp, well-defined peaks due to their more uniform texture. Charge–discharge measurements indicated that the thin films on SS substrates had higher utilizations but lower capacity retentions, while the thin films on SOS substrates had lower utilizations but better capacity retentions. We believe that the thin film with random orientation has faster mass transport of lithium ions while the thin film with preferred (0 0 3) orientation has better structure stability.