Preparation Of Lithium Cobalt Oxide Film Employed As Cathode Of Thin-Film Lithium Batteries

The thin-film lithium battery should be one of the most useful microbatteries in the future. The key part of this battery is the LiCoO₂ film as the cathode film, which has high voltage stage, high energy density, and stable charge/discharge ability. Furthermore the LiCoO₂ film is the chosen material commercially. In this article, by rf sputtering the LiCoO₂ film was produced. By hot pressing and cold pressing (and sintering), the LiCoO₂ targets used in the rf sputtering were produced differently. Both technics of the preparation of the LiCoO₂ film and the LiCoO₂ target were studied.By hot pressing, the LiCoO₂ target was produced. Different moulds were used in the hot pressing including the graphite mould and the SiC mould. By the SiC mould, the pure and high density LiCoO₂ target was produced. The density of this target was 5.21 g/cm3, which was 94% of the theoretic density of the LiCoO₂。In cold pressing and sintering process different percentage of binder were added to the target and the best percentage was found. While adding 1% binder the preferable target was produced, and the density was 4.89g.cm-3, which was 88% of the theoretic density of the LiCoO₂ With Ar as the sputtering gas, the technics of rf sputtering to produce the LiCoO₂ film were studied systematically. The best conditions to produce the LiCoO₂ film were that the power of r.f sputtering was 80w, the flux of Ar was 20sccm, and the pressure was 15mtorr. By comparing the XRD charts of LiCoO₂ films produced with different ratio of Ar/O2, the preferable ratio was determined, which was 3/1. With Ar/O₂(3/1) as the sputtering gas, the technics of rf sputtering to produce the LiCoO₂ film were studied systematically. The best conditions to produce the LiCoO₂ film were that the power of rf sputtering was 75w, the flux of Ar/O2 was 28sccm, and the pressure was 15mtorr.The influence of thickness, kinds of rf sputtering gas, flux of gas, and gas pressure to the produced LiCoO₂ film was studied, which affected the preferable orientation of the crystal. For the films thicker than 1.5μm, the preferred orientation was (101) and (104) plane.. For films thinner than 1μm, the preferred orientation was (101) and (104) plane while the sputtering gas was Ar only, and the preferred orientation was (003) plane while the sputtering gas was Ar and O2 mixing. This is because of the excessive O in the LiCoO₂ film produced by the Ar/O2 r.f...