Lithium cobalt oxide cathode film prepared by rf sputtering

Thin films of LiCoO2 prepared by radio frequency magnetron sputtering on Pt-coated silicon are investigated under various deposited parameters such as working pressure, gas flow rate of Ar to O-2, and heat-treatment temperature. The as-deposited film was a nanocrystalline structure with (10 4) preferred orientation. After annealing at 500-700degreesC, single-phase LiCoO2 is obtained when the film is originally deposited under an oxygen partial pressure (P-O2) from 5 to 10 mTorr. When the sputtering process is performed outside these P-O2 values, a second phase Of Co3O4 is formed in addition to the HT-LiCoO2 phase. The degree of crystallization of the LiCoO2 films is strongly affected by the annealing temperature; a higher temperature enhances the crystallization of the deposited LiCoO2 film. The grain sizes of LiCoO2 films annealed at 500, 600 and 700degreesC are about 60, 95, and 125 nm, respectively. Cyclic voltammograms display well-defined redox peaks. LiCoO2 films deposited by rf sputtering are electrochemically active. The first discharge capacity of thin LiCoo(2) films annealed at 500, 600 and 700degreesC is about 41.77, 50.62 and 61.16 muAh/(cm(2)mum), respectively. The corresponding 50th discharge capacities are 58.1, 72.2 and 74.9% of the first discharge capacity. (C) 2003 Elsevier B.V. All rights reserved.