Effect of annealing temperature on structure and electrochemical properties of LiCoO₂ cathode thin films

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• 作者：Zhimin YANG ; Guangjian XING ; Jian YANG ; Changhui MAO ; Jun DU
• 关键词：LiCoO₂ thin film ; annealing temperature ; structure ; electrochemical properties
• 刊名：Rare Metals
• 出版年：2006
• 出版时间：December 2006
• 年：2006
• 卷：25
• 期：6, Supplement 2
• 页码：189-192
• 全文大小：708 K

文摘

LiCoO₂ thin films, which can be used as a cathode material in microbatteries, were deposited using radio frequency (r.f.) magnetron sputtering system from a LiCoO₂ target and in an O₂ + Ar atmosphere. The films were characterized by various methods such as XRD, SEM and AFM. The LiCoO₂ films were annealed in air at 300, 500, 700 and 800 °C respectively. The effect of the annealing temperature on the structure, the surface morphology and the electrochemical properties of the films were investigated. The LiCoO₂ thin film deposited at room temperature is amorphous and has smaller grain size. With increasing of annealing temperature, the crystallinity of the films is promoted. When the annealing temperature increases to 700 °C, the films have a perfect crystalline LiCoO₂ phase. The LiCoO₂ thin film without annealing has no discharge plateau and small discharge capacity (about 27 μAh·cm⁻²μm). The discharge capacity increases with the increasing of annealing temperature and reaches 47 μAh · cm⁻²μm for the film annealed with 700 °C, which also shows the typical discharge plateau of 3.9 V. The cycle performance of LiCoO₂ thin films of as grown and annealed at different temperatures were studied. In the case of the film without thermal treatment, the capacity fading is much faster than that of the film annealed at different temperature, showing about 40 % capacity loss only after 25 cycles. However, in the case of the film annealed at 700 °C, the capacity reaches to steady state gradually and maintained constantly with cycling. After 25 times cycling, the discharge capacity of the film annealed at 700 °C decreases to about 36.9 μAh·cm⁻²·μm, only 0.8 % capacity loss per cycle.