Effect of Film Thickness of Layer-Structured Oxide Thin Films on Lithium Insertion/Extraction and Semiconductive Properties

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LiMィイD2xィエD2OィイD2yィエD2 (M=Mn, Ni, Co) thin films were fabricated by dipping Au wire into the citric complex during the synthesis process (DICC method). Only the LiCoOィイD22ィエD2 thin film was obtained by the in situ oxidation in molten carbonate. However, DICC process enabled us to fabricate the LiCoOィイD22ィエD2, LiMnィイD22ィエD2OィイD24ィエD2 and LiNiOィイD22ィエD2 thin films onto the Au. In case of LiCoOィイD22ィエD2 and LiNiOィイD22ィエD2 thin films, lithium extraction was easy but hard to insert lithium it. On the other hand, lithium extraction/insertion was quite easy for LiMnィイD22ィエD2OィイD24ィエD2 thin film up to 1 V/s scan rate in cyclic voltammetry with excellent cyclability. This result is really amazing that the charging/discharging rate of theoretical capacity within 10 seconds is possible principally but the recent state-of-the-art battery technology needs an hour. However, similar reversible charging/discharging reaction was obtained at very slow scan rate (0.01 mV/s) when the composite electrode o … More f LiMnィイD22ィエD2OィイD24ィエD2 was applied. This difference is a clear indication that the carbon conductive additive in the composite electrode enhances the electronic conductivity of active materials and passivated film formed on the Al current collector. However, it makes no potential gradient inside the active material, and hence it reduces the lithium ion conduction inside the solid phase. In case of thin film electrode, potential difference between electrolyte solution and current collector exists at the active material, and this enhances the lithium ion conductivity inside the active material solid phase.Optical current measurements were carried out using lock-in amplifier synchronized with the optical chopper. Unfortunately, we could not observe any traces of optical current. However, the formation of barrier type AlFィイD23ィエD2 passivation film was found at the Al current collector in the organic solution with LiPFィイD26ィエD2 and LiBFィイD24ィエD2 electrolyte by the high-potential field mechanism, which was similar to the anodic oxide film formation in aqueous solution. Less