Fabrication of LiCoO2 cathode film for thin film battery by Aerosol Flame Deposition

Abstract

Rechargeable thin film battery becomes an important power source for various small electronic devices to electronic devices such as micro-electro-mechanical system, smart card, medical appliances, and so on. Several thin film micro rechargeable battery systems were demonstrated successfully, and its necessity has been grown with the advent of nano devices and ubiquitous age. To realize the thin film battery, solid electrolyte, cathode, and anode layers have to be developed to the satisfactory level of performance. In the market oriented viewpoint, the cost for the fabrication of these micro or `mini` battery cells is not negligible issue and it should be considered from the initial stage of process development. In this study, the new inexpensive deposition method is suggested to prepare LiCoO2 cathode film for `mini` battery cell fabrication. The cathode material for thin film battery as well as bulk type battery has been chosen to LiCoO2 without hesitation since its performance as a cathode is excellent and its advantages, such as high operating voltage, high specific capacity, long cycle-life [1-5], are evident. In this study, we employed the completely new method to synthesize the oxide cathode, which is called "Aerosol Flame Deposition (AFD)" method. In the deposition process, single or multi-component amorphous oxide nano particles (soot) are synthesized by supplying metal halide sources such as chloride in the form of gas into oxy-hydrogen flame. The deposited film composed of synthesized nano particles is subsequently consolidated into solid film by high temperature heat treatment. The whole processes are carried out under normal air atmosphere with only optional control for moisture. The Aerosol Flame Deposition (AFD) was applied to fabricate film cathode of LiCoO2. The cathode of LiCoO2 soot was fabricated from aqueous precursor solution by Aerosol Flame Deposition (AFD). The aqueous precursor solution of the lithium nitrate (0.1mol) and cobalt acetate (0.1mol) was atomized with an ultrasonic vibrator (1.7MHz) and the atomized droplets were subsequently carried into the central tube of the torch by flowing dry Ar gas. LiCoO2 were formed by oxy-hydrogen flame and deposited on substrate placed in rotating stage, which was kept at 150°C to eliminate H2O produced during hydrolysis. The deposited film composed of synthesized particles is subsequently consolidated into crystallization by high temperature heat treatment at 500°C and 600°C for 2h. Fig. 1 shows XRD patterns of the as-deposited LiCoO2 and sintered at different temperatures. Figure shows that the crystallinity of as-deposited soot powder is already excellent, if considering that the specimen is thin. Compared with the as-deposited LiCoO2, the FWHMs of the peaks were obviously reduced and their intensity increased as the sintering temperature increased, which is due to improved crystallinity. The cross section of thin film LiCoO2 before the consolidation process is shown and the thickness of film was about 10 ?m in Fig. 2.