Influence of Two-Step Heat Treatment on Sputtered Lithium Cobalt Oxide Thin Films

A crack-free LiCoO2 thin film with a preferred oriented crystalline structure is obtained by adopting a two-step heat treatment with a combination of substrate heating at 300°C during sputtering and a rapid thermal annealing (RTA) process. The performances of cells deposited at room temperature and at 600°C with and without the RTA process are also compared. The LiCoO2 cathode thin film deposited at 300°C with RTA shows a high specific discharge capacity of 65 μAh/cm2-μm at a 1C rate and excellent reversibility of the dQ/dV curve in a half cell using liquid electrolyte. In a Li/Lipon/LiCoO2 structure, a specific discharge capacity of 63.5 μAh/cm2-μm is demonstrated, corresponding to 92% of its theoretical value. During charge and discharge the first specific discharge capacity of 60 μAh/cm2-μm is observed even at a 5 C rate, demonstrating superior cycling performance over 500 cycles with no capacity degradation.