Sputter deposition and characterization of lithium cobalt oxide thin films and their applications in thin-film rechargeable lithium batteries

摘要

Li Co oxide thin films were deposited by rf magnetron sputtering of a LiCoO(sub 2) target in a 3:1 Ar/O(sub 2) mixture gas. From proton-induced gamma-ray emission analysis and Rutherford backscattering spectrometry, the average composition of these films was determined to be Li(sub 1.15)CoO(sub 2.16). X-ray powder diffraction patterns of films annealed in air at 500-700 C were consistent with regular rhombohedral structure of crystalline LiCoO(sub 2). Discharge curves of thin film lithium cells with amoprohous LiCoO(sub 2) showed no obvious structural transition between 4.2 and 1.5 V. Shape of discharge curves of cells with polycrystalline cathodes were consistent with a two-phase voltage plateau at (similar to)3.9 V with a relatively large capacity and two additional smaller plateaus at higher voltages. Cells with the 700 C annealed cathodes showed a capacity loss of (similar to) after 1000 cycles between 4.2 and 3.0 V.