Thin-film rechargeable lithium batteries with amorphous and crystafline LiCoO2 cathodes were investigated, The lithium cobalt oxide films were deposited by radio-frequency (RF) magnetron sputtering of an LiCoO2 target in a 3:1 Ar/02 mixture gas. From proton-induced -y-ray emission analysis (PIGE) and Rutherford backscatterung spectrometry (RBS), the average composition of these films was determined to be Li115CoO216 or, within experimental uncertainty, LiCoO2 + 0.08 Li20. The x-ray powder diffraction patterns of films annealed in air at 500 to 7 00°C were consistent with the regular hexagonal structure observed for crystalline LiCoO2. The discharge curves of the cells with amorphous LiCoO2 cathodes showed no obvious structural transition between 4.2 and 2.0 V, while the discharge curves of the cells with polycrystalline cathodes were consistent with a two-phase potential plateau at -3.9 V with a relatively large capacity. Two lower capacity plateaus were observed at ---4.2 and 4.1 V with the 600 and 700°C annealed cathodes; the -dq/dV peaks were broader and weaker for the 600°C annealed cathodes and were not present at all with the 500°C annealed films. The chemical diffusion coefficients of Li in the cathodes obtained from ac impedance measurements at cell potentials of -4 V ranged from ,1012 cm2/s for the as-deposited amorphous cathodes to --10 cm2/s for the films annealed at 700°C. The capacity loss on extended cycling of the thin-film cells varied with the crystallinity and thickness of the cathodes and with temperature. With the highly crystalline, 700°C annealed material, losses on cycling between 4.2 and 3.8 V at 25°C ranged from 0.0001%/cycle (>1O cycles) to 0.002%/cycle for cells with cathodes from 0.05 to 0.5 m thick.

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Thin film of the title cathodes deposited by RF magnetron sputtering on a LiCoO2 target, consists of LiCoO2 + 0.08 Li2O as shown by proton-induced γ-ray emission analyses and RBS. Annealing of the as-deposited x-ray amorphous films in air at temp. from 500 to 700 . degree.C results in the formation of polycrystalline material with the same hexagonal structure and comparable electrochemical and electrical transport properties observed for bulk LiCoO2 prepared at high temperatures. Cells with the 700 • C annealed cathode films show good cathode utilization and discharge rates up to 1 mA/cm2 and excellent reversibility with capacity losses of 0.001 to 0.002 %/cycle for 0.2-0.5 µm thick films at 25 • C. Capacity losses on cycling, varying with the crystallinity and thickness of the cathode and the temp. are caused by an increase in cell resistance. -(WANG, B.; BATES, J. B.; HART, F. X.; SALES, B. C.; ZUHR, R. A.; ROBERTSON, J. D.; J.

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