Direct fabrication of LiCoO ₂ film electrodes using soft solution-processing in LiOH solution at 20 - 200°C

Application of Soft Solution-Processing, which is defined by environmentally friendly processing using (aqueous) solution, to the field of rechargeable lithium microbattery has been demonstrated by fabricating LiCoO ₂ film on the cobalt metal substrate in LiOH solution under hydrothermal condition. The film formation mechanism could be interpreted in terms of chemical dissolution of cobalt metal plate in LiOH solution at fixed temperature of 20 - 200°C, resulting in the formation of H _1-nCoO ₂ where n value increases with fabrication temperature and precipitation as LiCoO ₂ by heterogeneous nucleation on the substrate followed by crystal growth. The crystal structure and film properties have been characterized by X-ray diffraction, X-ray photoelectron, micro-Raman spectroscopic and scanning electron microscopic analyses. The films exhibited a good crystallinity despite the low reaction temperature without any post-synthesis annealing. The films prepared under different conditions showed different phase selection such as spinel (Fd3m) or hexagonal (R3-m), surface morphology and film thickness. An electrochemical activity of the LiCoO ₂ films was evidenced by cyclic voltammogram revealing a good reversibility on Li-intercalation and -deintercalation.