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 O2, and heat-treatment temperature. The as-deposited film was a nanocrystalline structure with (104) preferred orientation. After annealing at 500-700°C, single-phase LiCoO2 is obtained when the film is originally deposited under an oxygen partial pressure (PO2) from 5 to 10mTorr. 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 700°C are about 60, 95, and 125nm, respectively. Cyclic voltammograms display well-defined redox peaks. LiCoO2 films deposited by rf sputtering are electrochemically active. The first discharge capacity of thin LiCoO2 films annealed at 500, 600 and 700°C is about 41.77, 50.62 and 61.16μAh/(cm2μm), respectively. The corresponding 50th discharge capacities are 58.1, 72.2 and 74.9% of the first discharge capacity.
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